In reverse order
I once saw a trailer where the owner had used Slide out stablizers and somethign happened....suffice to say I do NOT under any circumstances recommend them.
Second "Something under the tires"
For the first couple winters I parked my Class A on crushed rock, nothing but crushed rock under the tires.
I did (the 2nd winter) put wood blocks 12x12 2" thick (well 1 1/2) under the jacks. Then when it came time to leave (Mid winter) I raised jacks, drove off and triesd to move the frozen to the ground blocks. no joy
So I broke out the 8 pound hammer and tapped them gently
Joy