I used Rustoleum on a number of planes, mostly big and small profile stunters. The main help at the time was the top price paints. One must avoid high humidity. 1st prime coat should be a tough autobody filler. Once that dries thoroughly sand it almost all off- progressively going from 200 grit to 400 and one more step if needed. I used a base color coat of white. That took the colored paint nicely, usually fairly thin coats. You can apply a clear epoxy or other finish coat but it really isn't necessary.
Rustoleum does take at least a month to actually cure solidly. A nice, warm, calm, dust-free room is ideal. If not, there are various ways to set up a paint booth to contain any overspray.
Phil C