Use MINWAX "Wipe On" polyurethane available at Home Depot. Using a Q-Tip, apply a thin coating over all the monocote seams. This keeps the seams from lifting and prevents fuel seepage under the seams. I have a monocote covered 6 year old Banshee with over 475 flights and the covering is still sealed with no fuel soaking. I also have a 4 year old Ultracote covered Pathfinder II with over 400 flights, see attached picture, and it is also still in fine shape.
DennisV