emjay
+1y
I have seen it before where some standard cab owners have cut the hump out of the back of their cabs and welded in flat sheet metal. This will give a bit of extra space to work with when making a custom box.
It is possible for you to make a flush piece to hug the back wall, that is what I plan on eventually doing with 2 8" Dynam Accoustic subs with a Nakamichi 300 II powering it. It's a small cab so a big, high powered setup isn't necessary.
I personally wouldn't do a cut through into the box because you would #1 have to do a superb job welding or face possible moisture issues, and #2 lose part of your bed. Much more work than is necessary for non-show.