Holy ****! That must have been a heart stopper!
I'm at a bit of a loss as to understanding how filling a tank, off the truck can lead to this, unless the support is rotted out. I can't imagine a manufacturer building a camper that can only be used when in the truck. To me one of the big features is being able to have your vehicle to use, when camping, without having to bring along the camper to go sight seeing, etc. And if boondocking, not having use of any of various tanks capacities just seems crazy disappointing and counter intuitive to a TC.
Your camper isn't that old. Was there rot or damage that lead to this?
Thanks for posting! :C