ORIGINAL: papermache
Go with the Solartex. I've used both solartex and koverall and solartex is MUCH easier to work with. Koverall requires that you prepare the surface, dope it on, seal the weave, etc, etc and by the time you've done that, you've added enough weight in dope to make it heavier than solartex. With the solartex, you can paint it with just about anything and then put a sealer coat over that and you're done. Good luck.
concur with papermache. having used both, i prefer solartex due to ease of use. just make sure you use a "cool" iron to apply it or it will wrinkle and never come back. another thing not mentioned is that koverall tends to fray since there's not an adhesive backing whereas the solartex doesn't.