Yes that sounds like the right approach. Unless you have very poor mounts on body to frame the body is not going to completly seperate from frame, unless it is a very bad accident. Lets hope that never occurs. I may have been a little over zealous in stating the point. I have seen guys bring cars to the track with belts bolted to the floor, and tech officials let it slide. And in a stock car you know you will get hit, sooner or later. So if I was, I surly didn't mean to be. I think with a fiberglass floor I probably would some sort of reinforcements, either plate, maybe 4 to 6 inches wide that extend from front to back of seat mounting points or some box type material, as room and your taste dictates. And this is probably redundant, I appoligise, use grade 8 hardware to mount seat and belts. If you use box under seat I wouldnt use a light gauge though, .120 min. wall and if thru tube of course use a welded in bushing thru tube. It sounds like you have a pretty good grasp of the principal. So nuf said.