Couple questions / comments:
1. Do you want the box removable? I ask as this would require the box to be small enough to exit one of the openings. If so, that limits you to a box 16" x 10.75" x 13" (roughly from the pictures). Taking away 1.5" for wood width, that leaves 14.5 x 9.25 x 11.5 = 1542.4375 in^2 or ~.9 ft^3. You should be able to find many subs to fit that. This is probably the easiest route as it doesn't entail any funky angles
1a. There are some box builders on either ebay or facebook (I think) that will build you something "custom" if you send dimensions. I don't know who they are, but you might be better off finding a local shop if you aren't comfortable building a rectangular box yourself. If you tell us where you're located, someone might be able to make a suggestion.
2. If you want maximum airspace and don't care about removing it, you can probably get another .25 ft^3 (total guestimate). Up to you if that would be important. Might be easier to have your subs play lower, but the built complexity and cost will drive up.
3. DEFINITELY have the boxes welded. Rivets are fine, but with bass bouncing around in there, it's bound to rattle.
4. Sound treat the shizzle out of the interior of the aluminum to avoid rattles.
5. H1 Hummers are cool. 👊 😆
I am certainly not an expert and there are many WAY more talented and knowledgable people on here that can probably advise you better, but this is my best guess without having the piece in my hands
1. Do you want the box removable? I ask as this would require the box to be small enough to exit one of the openings. If so, that limits you to a box 16" x 10.75" x 13" (roughly from the pictures). Taking away 1.5" for wood width, that leaves 14.5 x 9.25 x 11.5 = 1542.4375 in^2 or ~.9 ft^3. You should be able to find many subs to fit that. This is probably the easiest route as it doesn't entail any funky angles
1a. There are some box builders on either ebay or facebook (I think) that will build you something "custom" if you send dimensions. I don't know who they are, but you might be better off finding a local shop if you aren't comfortable building a rectangular box yourself. If you tell us where you're located, someone might be able to make a suggestion.
2. If you want maximum airspace and don't care about removing it, you can probably get another .25 ft^3 (total guestimate). Up to you if that would be important. Might be easier to have your subs play lower, but the built complexity and cost will drive up.
3. DEFINITELY have the boxes welded. Rivets are fine, but with bass bouncing around in there, it's bound to rattle.
4. Sound treat the shizzle out of the interior of the aluminum to avoid rattles.
5. H1 Hummers are cool. 👊 😆
I am certainly not an expert and there are many WAY more talented and knowledgable people on here that can probably advise you better, but this is my best guess without having the piece in my hands