I've had an Eagle Cap 1150 and the tank DID push to bottom out. (2005) The fresh water tank was supported by plumbers tape!
I have an Arctic Fox and the bottom under the fresh water tank is supported by TWO aluminum frame cross members.
The aluminum cross members look as if they have sagged under the weight of the fresh water tank (I've had the bottom off the camper to dry it out due to a water hose leak soaking) when I looked at them.
So. . .MY recommendation for the Arctic Fox is not to worry about it too much. Just to be safe, keep support under the camper when it is off the truck and with a FULL tank of fresh water.
If you can't, don't worry too much. . .just use up the water and it will reduce the stress. . .