pira114 wrote:
To be clear, the reason so many say not to travel with water in the tank is just to save weight.
That, and the fact that tank support in many trailers is often sadly inadequate, creating the possibility of the tank actually falling off. :E My own brand new 2014 Coachmen Freedom Express was a case in point - first time I filled it the tank sagged noticeably.

So I had my dealer fabricate and install a pair of metal support beams which solved that problem entirely.

I normally travel with 1/3 to 1/2 tank of water but can at any time travel with a full tank with no concern the tank may drop off the trailer. Since this is a much more common issue than many realize it would behoove
every RV owner to check their own rig for adequate tank support before traveling with it full. An enclosed underbelly makes this more difficult but when compared to having a tank fall off on the highway somewhere, well worth the effort. ;)