1988-1998 Chevrolet Silverado 1500 / Sierra 1500 Subwoofer Box Fitment

1988-1998 Chevrolet Silverado 1500 / Sierra 1500 GMT400 — subwoofer box fitment

What we researched for this specific generation: where an enclosure actually fits, what the factory speakers are, how the factory audio is wired, and which real builds and commercial products exist for it. Confidence badges say how well each figure is sourced — this is research, not manufacturer spec.

Body styles covered: Regular Cab, Extended Cab

Where a box actually fits

These are researched envelopes, not a guarantee. Measure your own vehicle — the numbers here tell you what to expect, not what you have.

Extended Cab Likely

Location	under the rear seat, extended cab
Outer bounding box	No independently measured dimensions found. Largest extended-cab products: NET Audio 55 x 13.5 x 10.5 in (as printed; axes not labelled; 1.83 cu ft, 6 in mounting depth); Sound Off Audio width 49 in.
Known obstructions	Jack (and toolbox) storage under the rear seat (NET, Zenclosures, Sound Off Audio); Zenclosures notes 1.25 in clearance under the box.

Regular Cab Likely

Location	behind the bench seat, regular cab
Outer bounding box	No independently measured dimensions found. NET Audio 61 x 9 x 17 in and 61 x 17 x 9 in (as printed; axes not labelled) for the deep and shallow boxes.
Known obstructions	NET: may not fit with a center console.

Door speaker fitment

Sizes and depths below are what research turned up for this generation. Confirm against your own vehicle before cutting or ordering — trim levels vary.

Front doors Unconfirmed

Factory speaker size	no maker or Metra source read for door speaker size or location
Adapter bracket needed	unconfirmed

Rear doors Unconfirmed

Adapter bracket needed	unconfirmed

Factory audio integration

Factory amp / premium audio	no GM document read for 1988-1998

Mounting locations

Extended Cab Unconfirmed

under the rear seat (jack and toolbox side)

Box makers: extended-cab boxes fit under the rear seat; NET and Zenclosures say the jack (and toolbox) have to be removed or avoided; half-width boxes leave the other side free. No GM dimensions found.

Regular Cab Unconfirmed

behind the seat (bench seat)

NET: standard-cab boxes sit behind the bench seat and "may not work if your truck has a center console". No GM dimensions found.

Builds and products found for this vehicle

Outside links. Some are commercial products, some are owner builds posted on forums — the label says which. We do not endorse any of them.

NET Audio (ported) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Dual Large Ported". Fit years stated on the page: 1988-1998. Published outside dimensions: 55 x 13.5 x 10.5 in (as printed; axes not labelled). Published volume: 1.83 cu ft. Mounting depth 6 in. Under the rear seat of the extended cab; one 10 or 12 in sub or a pair of 8 in; tuned about 34-37 Hz. NET says it also fits the GMC Sierra extended cab.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Dual Large Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 55 x 13.5 x 10.5 in (as printed; axes not labelled). Published volume: 1.83 cu ft. Mounting depth 6 in. Under the rear seat; one or two subs of 8, 10 or 12 in; 52 lb.
NET Audio (ported) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Dual Small Ported". Fit years stated on the page: 1988-1998. Published outside dimensions: 55 x 13 x 11 in (as printed; axes not labelled). Published volume: 1.2 cu ft. Mounting depth 5.375 in. Under the rear seat with the toolbox and jack storage removed; one 8 or one 10 in sub; 53 lb.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Dual Small Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 55 x 12.5 x 10.25 in (as printed; axes not labelled). Published volume: 1.2 cu ft. Mounting depth 5.375 in. Under the rear seat; one or two 8 or 10 in subs.
NET Audio (ported) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Single 12 Ported". Fit years stated on the page: 1988-1998. Published outside dimensions: 27.125 x 13.5 x 10.5 in (as printed; axes not labelled). Published volume: 0.8 cu ft. Mounting depth 6 in. Half-width, under the rear seat; one 12 in sub (also 8 or 10 in); tuned about 34-37 Hz; 33 lb.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Single 12 Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 27.125 x 13.5 x 10.5 in (as printed; axes not labelled). Published volume: 0.8 cu ft. Mounting depth 6 in. Half-width, fits alongside the toolbox and jack storage; one 12 in sub (also 8 or 10 in); 28 lb.

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NET Audio (ported) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Single Small Ported". Fit years stated on the page: 1988-1998. Published outside dimensions: 27.125 x 12.5 x 10.25 in (as printed; axes not labelled). Published volume: 0.7 cu ft. Mounting depth 5.375 in. Half-width, under the rear seat; one 8 or 10 in sub; tuned about 34-37 Hz; 31 lb.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Extended Cab Sub Box Single Small Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 27.125 x 12.5 x 10.25 in (as printed; axes not labelled). Published volume: 0.7 cu ft. Mounting depth 5.375 in. Half-width, under the rear seat; one 8 or 10 in sub; 26 lb.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Standard Cab Sub Box Deep Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 61 x 9 x 17 in (as printed; axes not labelled). Published volume: 2.93 cu ft. Mounting depth 6.325 in. Standard cab with bench seat, behind the seat; 1 to 3 subs of 8, 10 or 12 in; "may not work if your truck has a center console"; 80 lb.
NET Audio (sealed) off-the-shelf
NET Audio "1988-1998 Chevy Silverado Standard Cab Sub Box Shallow Sealed". Fit years stated on the page: 1988-1998. Published outside dimensions: 61 x 17 x 9 in (as printed; axes not labelled). Published volume: 1.91 cu ft. Mounting depth 4.385 in. Standard cab with bench seat, behind the seat; single or dual 8, 10 or 12 in; may not work with a center console; 65 lb.
Sound Off Audio (sealed) off-the-shelf
Sound Off Audio "1988-1998 CHEVROLET and GMC EXTENDED CAB TRUCK DUAL SUBWOOFER BOX". Fit years 1988-1998. Outside size: width 49 in; mounting depth 5.25 in; "0.8 cu ft per chamber". Sealed; two 8 or two 10 in subs; "jack removal necessary".
Zenclosures (sealed) off-the-shelf
Zenclosures "Chevy Silverado & GMC Sierra Extended Cab 1988-1998 Dual Subwoofer Box (UTS - Fits Under Seat)". Fit years 1988-1998. Outside dimensions not printed. "Approx. 0.75 cu. ft. Per Sub/Side". Mounting depth 5.25 in (based on a 6.00 in magnet). Sealed, down-firing; "Jack Must Be Removed"; 1.25 in clearance under the box; 2 x 8 or 2 x 10.
Zenclosures (sealed) off-the-shelf
Zenclosures "Chevy Silverado & GMC Sierra Extended Cab 1988-1998 Single Subwoofer Box (UTS - Fits Under Seat)". Fit years 1988-1998. Outside dimensions not printed. "Approx. 0.75 cu. ft. Per Sub/Side". Mounting depth 5.25 in. Sealed, down-firing, fits on the driver's side; one 8 or 10 in sub.

Build it for this vehicle

Design a box for this vehicle — Enclosure volume, port tuning, and a cut sheet.
Door speaker fitment — No measured door depth on file for this vehicle yet, so there is no fit check to run. The page says how to request one.
See the factory speaker locations — Factory speaker sizes, depths and locations we have researched for this vehicle.

Each link opens the tool with this vehicle already selected.

Before you cut anything

Measure your own vehicle. Trim levels, factory subwoofer options, and mid-generation changes all move these numbers, and a box cut to a researched figure that does not match your truck is wasted wood. Where a badge reads Unconfirmed, treat the value as a starting point for your own measurement, not as an answer.