If I am building the kit from scratch, I'll cover the gaps in the same color I am covering with (I use monokote, btw). But if I get a kit already built, or an ARF, I'll use clear monokote to seal the gaps. I keep a roll of clear monokote around for doing this and for covering graphics on the plane (I use my computer and inkjet pringer to make custom graphics for the plane). The clear monokote does a great job sealing the graphics (and the gaps too).