Sarlacc, I painted my rubies vinyl helmet last year using mostly Rustoleum, and it worked pretty well. Make sure you lay down a solid coat of primer (get the expensive Rustoleum Premium). Just be aware that vinyl warps in heat. When you leave it outside to dry, it's gonna change shape a little. The Don Post 95 is thicker and more solid than Rubies, but you still might have trouble. Then when you heat to reshape it, your paint may bubble up if you get it too hot. I really wish I hadn't painted mine in the middle of summer... it led to a lot of extra work. Although I still would have had to reshape it in the hotel at Dragon*Con with a hairdryer because my friends who drove it there had it in the back of the car, under a window in the sun for the entire 6 hour trip.
Darth, I'm actually working on a Sgt Fang right now and was trying to decide if I should buy earcaps and range finder (still haven't researched who's currently making them) or just try to make them myself from sintra using the WOF templates. If you've got any of those parts laying around and sarlacc doesn't take em, shoot me a PM.
No rush though, I've got a lot of cleanup to do on this thing. Also, I think I'm gonna paint before putting the earcaps on. That'll be a lot less masking to do.