Next step is to install the 1/8" ply base onto the rails which were put in when the fuse sides were being laid up. It is stuck in with RTV (I had black on the bench). I don't worry about fuel proofing it, since it can be pulled out and scrapped if there's a problem. The fuse sides did get a coat of epoxy on them, plus paint spray.

Second photo shows the tank, nicely nestled in a bed of wrap-around foam, with the fuel lines going through the firewall cutout.