I`ve never been stuck either and whenever i park on grass i always use grip mats even in summer.
A particular C&CC, T.H.S. held on the field behind Bodnant Caravan Park, Llanrwst springs to mind several years back.
When we arrived the grass on the field had not been cut and was very very long although it was bone dry with absolutely glorious sunshine and very warm.
I still got the grip mats out and parked on them, took me a couple of minutes longer than parking up without them.
Quite a few people found it very entertaining and laughed openly, i took not notice.
We was there for the weekend and when we came to leave on the monday morning there had been a ridiculously heavy dew overninght, the grass was dripping.
Many many motorhomes and cars with caravans were really struggling to get going because as soon as the clutches bit their wheels started spinning.
Revving the bollocks off them to get the wheels going as fast as possible like a lot were doing just makes things worse.
The stewards along with a couple of other 4 X 4 owners started towing people off the field.
Then came my turn, i refused the offered tow, i rocked the motorhome with the clutch a few times keeping the wheels on the mats then smoothly drove off.
The momentum i`d created by rocking carried us onto the hardstanding at the entrance to the field where i`d stopped, got out and walked back for the grip mats.
A few people came over and asked if they could borrow the grip mats to which i openly laughed and walked off with mats in hand.
Whilst you can get stuck in deep mud wet grass can be just as bad and once the wheels start spinning you lost the battle.