I don't really like the asphalt-type undercoatings, they really do a great job of holding moisture in, but not so good a job of keeping it out in the first place. I wouldn't use it unless your car has already been treated with it, because once it's on there there's no going back, and I prefer to be able to see rust spots and treat them before they develop into a hole that's hidden under a layer of goo. There's a product from Dominion Sure-Seal - I think it's simply called Dripless Undercoating - that seems harmless to rubber & plastic. Dries to a waxy finish, it seems alot like the stuff Crown uses. Pretty cheap too - I think it's sold through NAPA. My 740's been loaded with the stuff, and it seems to stick fairly well, though it'll still wash out of the wheelwells & off the floor pans eventually.
--
Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina