Last pair I did I mitered the corners after seeing Peters results. I did not go with the beveled edge, not my thing. I used to cut the pieces deep enough so they went from baffle to front edge, then I'd cut and inch or so of foam off and notch the inner corners where needed for wiring. Now I've been cutting the pieces an inch short so they don't butt up against the baffle, leaves woofer and wiring clearence.
As Peter and Mike said, all wiring is done prior to no rez, it's the last step. When I install it, I do the 2 sides of each cabity, then the base & top. I put a bit of an arc in the last 2 pieces of no rez then butt it into one corner and work my way across to the other. first piece was a little eawkward but you get the hang of it iquickly.
Pieces were also cut just a hir short to get a good fit in the corner.
There's a pic over in the flat pack thread if interested in the mitered corner with no bevel look.