Hi Redza,
I initially rivetted it all together, to help getting all the levels and design right.I started by putting a rivet through the aluminium angle & into the rib of the boat. I did this for 3 pieces running across the boat & then used a few bits of flat aluminium as joining pieces, for the angle running from front to back. Once I was happy with the design I got it welded, although it all felt solid, I don't think the rivets would stand up to the pounding that a tinny gets over time.
I also used standard 12mm ply, which I painted with an oil based undercoat to seal the wood & stop it from bending or rotting. Carpet was the glued on with a contact adhesive.
Hope this helps !
regards
Craig