Well I'm back from RVator's where I've been assembling my xtra. I solved the tank issue thanks to help received here. RV removed the tank from his US 60 and it was a Dubro 12oz and small enough to fit perfectly. I pulled the fuel tubing through the firewall and connected to the tank, eased the mount into the slot behind the firewall and screwed it down with allen head machine screws. I then trimmed the belly pan, marked the spot for the wing bolts and used a rotobroach to cut the holes. I didn't know how well it would work on plastic but it cut two holes big enough for hex head 1/4-20 plastic bolte to pass through as cleanly as if they had been molded in. Not a single burr even. It's glued and drying. I connected the aileron control rods while it dries. Here's some pics of the work in progress.