Provided caravan is just stored with corner steadies lightly on the ground without stressing body you will be ok. It is preferable to leave handbrake off with wheels chocked.
I don't think it will actually cause any structural damage to the caravan but what I would be more concerned about is the fact that the ammonia in the fridge not being level could cause problems with the fridge operation in the future. I do know that the fridge has to be level when pitched but whether this will have any detrimental effect when stored I'm not sure. Couldn't you place some short planks under the one wheel then put some wooden blocks under the front and rear legs to eliminate the gap as this would solve your problem.
We have stored our caravan on a sideways sloping hardstanding for nearly 20 years and never had any problems with the fridge or anything else. Our slope is probably less than 1ft.
Our caravan is also stored on our drive on a slope and we have never noticed any problems, I make sure that I do not put too much pressure on the corner steadies though, if in any doubt how about trying to level it up as a previous poster mentioned.
Ours is stored on a sideways slope, most of the time we level to the higher side of the slope. If we are tired we just slap it in sloped for a couple of days, never had a problem.
we kept our old 'van on the drive at home which also has a side ways slope, kept her on there for a couple of years ,never did her no harm,corner steadies just touching ground, handbrake left off, wheels chocked, fridge always worked well when we took the old girl out.
we would be keeping our latest 'van at home too if she wasn't too big to sit on the drive
------------- no tin tent outings booked as yet ,just another cruise in Sept' booked so far