I used 1/4 x 5/16" t-nuts on the underside of the seat pedestal. Once the floor is glassed in, I won't have access to the underside, so I can't use regular throughbolts, and I don't want to just screw the pedestal in. (that's how it was done before, and I think the reason it became so weak and wobbly, also leading to the rot in the floor). I just pushed them into the predrilled holes from above and lightly hammered them into place.