My Webesto rocks. First off, put the heater as far aft as possible, and the exhuast even farther aft. A couple whiffs of diesel exhaust will send anyone onboard hurling over the edge. The thermostat I have mounted on my dash, seems good there. I tried three of the 2" openings, it didn't move enough air to feed them, so stick with 2. Oh yeah, and they are a ***** to get primed, I finally just put my tank on the roof of the boat and turned it over untill the Webesto got it's prime, from there on in it was fine. They come with a little copper coil that goes in the exhaust hose to allow water out, cap the damn thing off and drain it manually, it LOVES to "chuff" a little exhaust into the cabin once in a while.
Otherwise, you are going to love it! And get ready to spend a lot of time priming it, my advice on top of putting the tank on the roof, I use a kicker priming bulb. Squeeze it untill it is hard, then put some vice grips on it to REALLY suqeeze it, the tiny little pump in the kit does not pass air very fast.