Warping can be a problem, especially with Balsa Fins. The use of Monokote, SolarFilm, Ultracote, and many other plastic model airplane-covering films have been used, at least since the 1970's.
This photo below is Martin Catt's ( DARS ) "Merlin" at NARAM-19, in 1977 ( Kansas City ) . . . He used Monokote on the Fins and as Trim.
The orange E Dual Egglofter to the right is mine, also at NARAM-19, powered by an FSI E60. Unfortunately, at that time FSI E60's were very cato-prone ( over 80% of them failed at NARAM-19 ) and the motor exploded, about 5 feet off the end of the rod.
Dave F.