I use regular white Eternabond and only use it over straight surfaces (edge of the roof meeting the wall, skylights, etc). Like dave said, the key is prep. I would remove any loose caulking and clean it however Eternabond suggests. I bought a spray can of the Eternabond primer when I did my last camper and just used that.
When installing the Eternabond, don't stretch it. If you stretch it, the bond and watersealing abilities are diminished. Once you have laid the tape, use a roller and roll it down with some good pressure to fully activate the adhesive. Once it is installed correctly, you never have to worry again =)!
For things like your air horns, the round holding tank vent, any ladder attachments etc you should probably stick with Dicor. Eternabond doesn't do that great around tighter curves. Dicor self leveling is the easiest and cheapest way to handle those, but remember that you need to inspect those way more often.
