I have tried sealers with mixed results, usually not the smooth surface I was looking for. Just breaking down and glassing the surface may be the easy way. I have been using the Deft Sanding Sealer for my glassing for a log time and like the ease of using it but just discovered something after blowing out a fuel tank seam with a YS engine and blowing 10 ounces of fuel through the fuse, it isn't as fuel proof as I thought it was. I almost never glass any glow powered planes but this is the one I did.
It lifted the glass from the inside out a little, more like bubbles.