"...These campers are designed to be fully used on and off the truck..."
Just to clarify that statement... it is most likely true for being in the cab-over per this discussion topic, but some mfgr's may not recommend use unsupported as in the case of the water tank- owners should check their specific model with mfgr's recommendations. IIRC there is a camper maker that does not recommend water in the tank when up on the jacks only- the weight could pop it out the bottom.
I sort of recall a member a few years back that had the tank fall out.
As a matter of personal best practices, I always drain the the domestic water tank and water heater as much as possible before lifting it off the truck even though my mfgr states acceptable use off the truck. I tend to err on the side of being safe as possible- I do not want that extra weight up high when loading/ unloading or using without full bottom support... JMHO.