I would use wooden steps(dramatically cuts down on trailer movement). Place 2x6 board under tires. I leave propane on when gone in case of a power outage, that way my fridge contents will be ok. Slideouts are fine left open during season. I also add stabilizers in front and rear of tires on the frame. I simply use 4 cheap auto triangle hand crank stablizers on cinder blocks and tighten to frame. Again cuts out alot of movement. I would recommend turning water off when you leave, but also use a surge protector on your a/c. Cinder blocks placed on sand will set in fine, just place a small board on top of block for your jacks to rest on.
On another note, alot of seasonals tend to want to leave their gray valves open to limit draining so often. At my park I advise against this for two reasons. If a clog in the park sewer system occurs below you, it has the potential of backing up into your tank and beyond when the campers above you flush tanks. Second, you will get sewer flies coming through all drains and out into the camper. They look like little nats.