I start at the bottom also, been doing that way for years. I've had a couple gaskets that were more like soft rubber like the stuff they sell for window run channels... they tear way too easy. It's more like foam than rubber.

68 Road Runner, 69 Belvedere, 71 Challenger Vert
340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z
66 GTO, 06 Magnum RT AWD. 07 Ram CTD, 07 Ram