Hi Alan,
Solartex is the best to paint on... because you don't need much preparation before painting !
So, that's great for lazy guys like myself ! :lol:
In fact, that depend of the effect you want to obtain.
Solartex, you have fabric texture, so, that will suit vintage models (planes and gliders).
For fiber glass type gliders, the best is to use Oracover. And you will have the plastic finish. Your B4 have certainly oracover on the wings.
The other method on foam wings, is to use epoxy and fiberglass. A it of filler and sanding and that's ready to paint, still with a smooth plastic finish.
Now, if you want to paint on oracover, you must prepare the surface by sanding the oracover (use water 1200 grain). Some use primer, but that's expensive. The sanding cost less... May be not for your harm ok..
Otherwise, your paint will not stay long on the model.
Then, you can varnish if you want, but that's not necessary on a glider.
Let me know if you have any questions, or if I'm not clear enough ! It's still early in the morning...
Need my coffee now !
Fred