Glue and clamp. Screws usually loosen overtime due to vibration unless you use some epoxy to keep it in. A well done wood glue job will basically be a permanent bond as if the wood is one whole piece.
Actually, I use screws(from the outside), glue, and clamps. Sometimes I'll use screws from the inside if I can't get a clamp on there. I use a light glaze of body filler(bondo) to smooth out and fill any small gaps between the 45's and box wall.
Sorry about the slow progress, the guy I was building the box for called and pushed the date back until after Christmas, so I set it to the side so I could finish couple of other boxes. I'll be finishing up the Gcon box today and I'll make sure to post more pics.
Building a nice looking box doesn't mean having to have fancy tools. It's all about how smart and creative you are with what tools you do have. When I first started, I had a table saw that the top was bent on and couldn't be squared. I had to do some ghetto **** to set up the fence, then clamp it in place and hope for the best.
My boxes still came out looking legit, you'd never be able to tell I used an old beat up table saw and sander that I found in my grandpa's basement. This was my first professional looking box and I still have this box 2 years later. Both the box and subs were stolen, but still made their way back.
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Sent from my G870a on 38's