I have an old Super Aeromaster fuselage covered in Koverall and have about four coats of Minnwax Polycrylic on it. What is the best way to sand this stuff for an absolutely smooth surface to paint. I did lightly sand between coats with dry 320 grit. But in certain light, there seems to be streaks in the side of the fuse that I am afraid will show after painting. Can this stuff be wet sanded or should I stick to dry paper and a couple more coats?

You can use wet and dry paper on it. I use polycrylic when I use fiberglass and it sands fine

It looks like that is ready to prime. It's the primer coat where you can really get fussy about making it perfect. Shoot a coat on, then sand nearly all of it back off. Use filler where you see the need, then prime again and said it smooth.

Jester is correct. I prime the surface & sand the primer to get a smooth finish. Also their is less chance of cutting thru the poly & into your covering once you see the covering comming thru the primer.....Gene

I like your idea, guys. I never thought of primer, but it sounds right. I will try it.

I have sprayed a very light coat of primer on the airplane and it looks like it could be painted without further steps. It is absolutely smooth. However, I am going to sand about 95% of this off and put a second light coat on it and see what it looks like then. I used Rustoleum auto primer. Don't know why priming it did not occur to me. A fit of stupidity, I guess. It was the absolute answer.

Forgot to upload a pic