I built a lot of foam wing planes the last few years and do not like the grain so I usually put on a watery slurry of Dap lite weight spackling, sand most off, completely coat with 50/50 diluted (with plain water) Tite bond or Elmer's wood glue...lightly sand and spray on just about any color I desire, mostly preferring the water based Creativ craft paints (cheap) but rattle can Rustoleum works as well with light coats initially
I have painted the inside of Doculam clear or the outside of SLC with good result
BTW a total coverage finish above the color using thinned Wood glue is fairly fuel proof but I still prefer to lay down a layer of SLC...lite, fuel proof, and glossy