The seal or not seal question also depends on the look you want. Solartex is completely flat as it comes off the roll, so it won't look like painted fabric. If that's what you're going for, you're all good. But if you want a slight luster to it like you'd expect on a Cub or Stearman, you'll want to hit it with at least a couple of coats of clear gloss. It still won't have the same look as doped fabric, but it will be much closer.