Arctic Fox says this under the heading of outdoor winter storage:
"Always support the camper at the corners and outside walls. IMPORTANT: You must support camper correctly as set out in the diagram (Page 21A). Incorrect placement of blocking will result in damage to the sub floor and/or waste and fresh water tanks."
For some reason the diagram referred to does not show up in the online Owner's Manual but according to my hard copy, they suggest stacking 2x6's until you have enough height to lower the TC until the jacks don't touch. They are to be placed running side to side at the front of the bottom, again in the middle and again 8' from the front. As I recall, I stacked 10 - 2x6 x 6' for a total of 15". I nailed them together and attached some straps to make them easier to move around.