Been there done that.
Moved to the West Coast of FL. Most of the region was flooded the month prior so we were able to see low lying areas, etc. when looking for a storage lot. Most of the lots around here are on grass/"soil". Very few gravel and fewer concrete.
Found a nice storage facility with a concrete drive but grass lots. 12x50 was only $66/month. They were dry during the storms and the soil appeared solid under foot. Most of the lots we looked at were still slightly soft under foot. NEVER take their word for it. "We have no problems with the big units, moving trucks, etc..." But the "moving truck" were rentals with a max loaded at 26k. The big units were 5rs. The other big RV is Class A/Gasser (35'). So repeatly tell them I am 43' and 40k. I recently scaled in at over 45k with toad.
I lined up for a straight back-in (while still on the concrete). The spaces are tight at 12' each. I got the back in centered but since the adjacient spaces were empty I was slightly off in the front. I turned the wheel slightly and pulled all the way forward. I got out to check alignment and noticed where the steer wheels were is now loose soil (approx 1"). I make a mental note not to turn the wheel on the soil and back in. This time I am off center by 6" in the back but straight. I pull forward, not turning the steering wheel until it is on concrete and stop. I put the MH in reverse but nothing happens. I cycle the parking brake and the transmission but nothing. I get out and see....
The "soil" was just a crust over sand backfill. I put the rear jacks on 2x12x36 and raised the rear. Clearing the sand in front and rear of the tires was easy but it was also easy to CLEAR UNDER THE TIRE. Wood was not going to help so I called roadside assist for a winch out. 2hrs later a medium (F750) tow truck arrived, strapped the rear hitch and we were able to winch/idle the MH out. I was happily surprised. The only damage is 1)some of the cloth covering on the aqua hot exhaust is off and while enroute to a different lot; 2)the ABS light came on.
SO, just because the ground is dry and firm doesn't mean it will hold a heavy DP. We are parked on concrete now.