I've recently been patching my old vinyl.. the conversation may be of use:
http://www.wanderthewest.com/forum/index.php?/topic/5113/
That patching material I've been using appears to stick extremely well. I'm about 3/4 the way through patching the whole thing. Which looks like it will be about three 5 foot rolls worth when I am done. My plan is to use the 303 stuff when finished patching.
My fingers are crossed. I find the idea of spending more on a new sideliner than I spent on the camper itself as well as the complexity of installing it to be very unappealing.