Box for 98' S-10 in bed

I have done this both ways.  If you decide to go with the rectangle cut out, make sure that you weld a frame around both the cab and bed made out of 1 x 1 square stock.  This will add strength back to the truck.  Then go to your nearest RV parts place and get a rubber boot that you can put across the opening of the cab and the bed.  This setup is nice for the reason that you can show off your subs and have relitive ease in maintenance.

If you want to go with ports through the cab into the bed.  I recommend that you  go with at least a 6-8" diameter holes.  Ideally you would want to figure out your air volume from the subs and use tht to make your decision for port diameters into the cab.  again I suggest that you weld a suport frame around the holes you cut and use the boot material.  You will also have to figure a way to do maintenance on the subs and box.

Make sure that the box is bolted not screwed, down to the bed.  You will also need to contend with weather proofing the box.  Treat the wood with a good oil base paint and then I would spray the box with that bed liner spray.  Covering the box with a material make pose a risk of water staying on the wood.  You should also use either foam or cylicone to stop up the bet channels that go under the box.

Best of luck,    and.....

Take your time and do it right the first time.

or you will be just wasting your time....