Yes 303 is the stuff, and my tonneau cover reps tell me that armor and sonofagun both have alcohol in it which is what dries out the vinyl.

I used to just use bleech white, but I have gotten back into shines. I love Mother's reflections tire care, it soaks in so there is no cast off, and it's not really glossy. It just looks like a new clean tire and doesn't do to bad about attracting dust.