My G3 has a diamond plate aluminum floor, probably about 1/8" thick. I got a piece of 1/2" plywood and cutout a piece about 18" square, so that it would overlap the ribs or other fastening points of the existing floor. I epoxy coated it just so it would never rot, then fastened it to the existing floor. Now when I installed the seat base, the stress was spread out over a large area. I'm 250#s, and it hasn't moved a bit. I'd look to see if you can do the same thing. If your deck is just thin aluminum, maybe you may want to go with 3/4 plywood. I could take a picture of what I did if you'd like.
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Shellback CVA 59 VF-74
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