I use 5 tiers of PT 6x6: There is 3/4PT attached to the bottom of the camper and 2 6x's - continuous in the long direction tiers, 3 each in the short direction. This is to fully support my camper when off the truck at home (I never take it off in the field.)
The lumber takes almost all of the weight as the jacks are there just to keep it all steady... just a crank or 2 on the jack the hit the ground. I feel this is very stable event though it it relatively tall. I do not need to go much higher when loading it on to the truck. I regularly get into the upper cab to access the upper cabs or make the bed,
![](http://i.imgur.com/6r9JLC9l.jpg)
I would recommend checking with the camper manufacturer on their take whether or not the TC can be unsupported with water, waste tanks.