building deck/floor up off the frame

I'm thinking of using a HF 4x8 for my 5x8 build. I know I'll have to make room for the tires but would there be any difficulties building the frame/floor/deck up several inches from the trailer frame. I don't know if i'm explaining this right but see if you can follow...
If the floor frame is built on like 2x2's with a 1/2' ply on top bolted to the frame could you build it with 2x4's with a 1/2' ply on top with the 2x4's on the long edge so the deck/floor would be 3.5' (plus a 1/2 for the ply) off the trailer frame instead of only 1.5 (plus ply). This would give me an extra couple of inches to clear the tires and lessen the impact on the sleeping area.
I guess the question is, if I can do it (I mean I know I could do it) would it be safe and could I get bolts long enough to go through the ply-2x4-frame?
Thanks, and Cheers,
David
If the floor frame is built on like 2x2's with a 1/2' ply on top bolted to the frame could you build it with 2x4's with a 1/2' ply on top with the 2x4's on the long edge so the deck/floor would be 3.5' (plus a 1/2 for the ply) off the trailer frame instead of only 1.5 (plus ply). This would give me an extra couple of inches to clear the tires and lessen the impact on the sleeping area.
I guess the question is, if I can do it (I mean I know I could do it) would it be safe and could I get bolts long enough to go through the ply-2x4-frame?
Thanks, and Cheers,
David