What about using fuel proof dope for fuel proofing?

By the way, congrats on the CA model. Maybe you could use a bigger engine and practise throttle control with it. I'm building a .40 sized CA Widebody and putting a Saito .72 on it. I'm using a Hitec 55 mini servo for throttle and Dubro foam wheels. Another weight saver is not using a tail wheel assembly. Those weigh a lot. I'm going to make a tail wheel with just wire. I may epoxy that into the rudder or put a screw into the fuselage for the wire to turn around. I won't use a collar, and will bend the wire 90 degrees instead to retain the wheel. Collars weigh a lot too.

I always cut down my axles after fitting the wheels and collars. That extra axle material weighs a lot if you hold it in your hand after cutting.