I scratched my wingtip today. I am new to this. Is it a good idea to paint the scratch with dope or use like thick CA, or is monokote the absolute way to do it?
I don't care so much about look, I want to make sure engine fuel does not eat up the balsa.

Thanks,

If you do not have some extra mono or ultra to cover it. Then the ever trusty, ever reliable, clear packaging tape will do.

If the plane is  foam construction don't use anything like laquers, or acetone or similar based paints on them. It will "melt" the foam.  The tape as previously suggested is the way to go if you can't match it otherwise.  Use something compatible and friendly to the materials used on the plane.  If in doubt, take it to the nearest hobby dealer and ask.

I have to agree with the packing tape, since you said that looks aren't important. I've put packing tape on minor dings that were in the exhaust path and I've never had it come off on its own. Just be sure to clean the area well (windex and paper towel) before you stick the tape on.