I've worn it under my Teknic Chicane Vented One-Piece Suit, for a few weeks, to work, in hopes to stretch out the suit and get use to it a little before the trackday weekend. The undersuit does wonders keeping me warm on those cool mornings, and doesn't feel like I'm wearing a thermal blanket either. I don't know how it works in the hot, but getting the suit on and off, like they state, is very easy.
Thanks for the replies, and suggestions.
Well I ended up buying a one piece PsycleSkins Undersuit from Sportbike Track Gear: