Hi fellow Bullet owner....
I would assume that you have the "Thermal Package" on your TT as you made mention of insulation. Don't get your hopes up in that regard. The coroplast is the only thing covering the underbelly. Been there, done that. The nice folks at Keystone responded to a question I had regarding the makeup of the Thermal Package and this is what it consists of; covered underbelly (coroplast), larger heater, and heated underbelly, accomplished by routing a 2" duct from the heater to the underbelly area close to the tanks. That's it. Little more than window dressing if you get into really cold temps.
Now, a word of caution when removing the coroplast by unscrewing the perimeter (which I did). On my Bullet one end of the fresh water tank rests on the frame. The same frame that the coroplast is screwed to. In the area of where the tank is the coroplast screws are shorter than the rest. Make sure you remember where those particular screws go when re-installing the underbelly. If you don't you will be dealing with another leak
! Trust me, I know this
.
Good luck finding your leak. I would advise that you double check everything that you can access from up above before going underneath. Would hate for you to go to all that work of removing the underbelly only to find your leak was above somewhere. Don't assume that because the water is coming out underneath that the leak is under there also. Open all the access panels, remove the shower faucet, etc. On my TT there aren't too many connection points in the underbelly. Most can be accessed from above.
Let us know what you find.