Susan
on my
Scamp I had spongy floor back by water tank drain, by the time I had screwdrivered all the softness out i had a probably 8 x 12 in area. I squared up the cuts with dremel and jigsaw. fitted in piece of plyboard (think like a jigsaw puzzle). I used a short strand
fiberglass mix to tack it in place on top, let that dry then went on bottom and laid that stuff on whole board and surrounding area. I finished with regular
fiberglass mat and resin on top, but you could just smooth out the short strand stuff on board and surrounding area on top also.
Scamps have no bottom to their cabinets, they are open, on mine the front screws kept coming out on the bottom (screwing into side of osb just doesnt hold or plywood for that matter) I used some 1 1/2 in aluminum angle, screwed to floor then cabinets screwed to that