Garage Floor Paint

X2 on the Vapor barrier and even Vapor permeable epoxy has it's limits. I have it (VP epoxy) in my basement and there are areas that have a cloudy patina from vapor being trapped under the epoxy. There are kits you install on your floor to test for vapor or water content prior to doing the floors and they are not terribly expensive. Well worth the money.

Lots of prep work and homework or you'll just be pissing money away.

http://www.epfloors.com/moisture-testing/

Good reading here.