When we still owned our Montana we had a similar problem. Our bedroom slide would come out while traveling, called the dealer and he had me check the fluid level which was slightly low but not bad. I added fluid and the problem went a away for awhile, then reappeared! After much searching the dealer found a loose fitting on the cylinder under our bed.
The OP's problem is most likely a leak somewhere the big question is where. I'd have a competent repair service look into the problem. It's fixable for sure.
Dan
