On my LT-40, I ultracoted the edge that the wings sit on. I have read of some people using sealing foam or something to keep out exhaust and fuel, but I did not do this fearing it would skew the way the plane sits on the fuse...

As far as the engine area, I covered it in thinned epoxy, then went over it with a gloss black fuel proof paint, looks real nice....I wouldn't put the monokote in there..