I use thinned epoxy like PTUlmer said - except that I put a drop of food coloring in the two-part mix for two reasons; one is (Hooray, ctrl-z works! I just hit escape too many times and my words came back like magic) that it helps make sure that you have mixed it thoroughly (just try it, you'll see). The other resaon is to provide color up from that comes close to whatever I was going to cover/paint the fuselage with. You can always find four color packages in the cake mix part of the grocery store (red, blue, green, yellow). At Easter time you might be able to find more color selection. The third reason is that you avois the yellowing effect if you use a dark shade. I have been doing this for at least 20 years. It does not weaken the epoxy in fact I would argue that it would minimize the effects of ultra-violet rays and moon beams.