I use Minwax polycrylic to seal all my fabric covered planes. I can brush it on, two coats and wet sand with 400 grit. I then use Rust-oleum primer to fill any minor faults and wet sand till I am happy with finish. Then I just use Rust-oleum spray cans to finish painting color on. Never had problem with gas powered planes. I am trying on new plane using Rust-oleum " universal bonding primer " PN#285011 to see how this works as it is made to bond topcoat to difficult surfaces, It cost more and not sure if it can be wet sander to a supper smooth finish for final painting. Will try out this weekend to see how everything work out. Also if you are using glow engines you could use a clear overcoat on Rusy-oleum to be supper safe.
Best part is water clean up with poly.and no Bad fumes of fire problems to worry about.