RE: covering and painting Spacewalker II
Brush marks will show on any surface if not done correctly. I think brushing requires more skill (by far) than spraying. Spraying latex should not be too difficult. You don't need high end spray gear. A small pancake compressor and a touchup gun should work fine. Or, a HVLP set up will work as well. It's just a matter of experimenting to get the mixture right. It needs to be thinned a bunch to work right. I would stay away from the brush unless you are dead set against spraying. I'm brushing on my dope because I live in an apartment and don't have a place to spray.
As for sealing the edge of the masking tape, I'll explain a little more. No matter how well you lay down your tape, there is going to be some paint that works its way under the mask making your nice line look like crap. So, to avoid this, first paint a thin coat of clear along the edge that is going to define the line so that the clear creaps under the tape. Use a small hobby brush so that you are applying a line about 1/8-1/4 inch wide along the tape with half on the tape and half on the covering. The clear will dry and keep the color coat from getting under the edge. I would recommend using the same kind of paint as the color coat. Not sure if you can get clear latex but if not clear water based varnish will work or you can take a piece of your Solartex to the paint strore and have them match it with latex. If you intend to keep this plane for a long time and use glow fuel, the only really fuel proof clear coat is two part epoxy. I used water based varnish to seal a firewall once and it softened rather quickly. I will not use it again for that. Two part epoxy is pretty easy to use and has great qualities like flow out and it doesn't tend to run. Just be very careful that you don't apply it too thick as it can really add to the weight in a hurry.
Andy