Here's another alternative that I use when I can. It is more time consuming, but I'll throw it out here anyway :-)

Put the two panels together at the desired angle. Use some blue masking tape or strapping tape to hold them together. Take two sheets of 60 grit PSA sandpaper disks and stick them together so the grit sides face out. Insert the sanding disk between the two panels and slowly sand the inside corners off. The panels will slowly come together at the correct bevel. I try to do a couple of feet at a time, removing and replacing the tape as I go. Make sure the panels stay tight against one another. After sanding, I fillet the inside and apply fiberglass tape. Eventually, the outside "knife" edge will be sanded, as Chip mentioned, to about a 1/4" radius.

My main reason for doing this is to get a clean looking edge. I doubt there is much strength loss or gain in the finished glassed structure. This is also the method I use to mate a deck and hull in both S&G and Strip boats.

Bill