Is it possible the blocks are squishy, meaning they have flexibility in them. Try using solid lumber once and see if that makes any difference. If so, it's the plastic blocks you are using.
Another thing, if you are parked on dirt and especially grass, any block you put under your tires or jacks will sink into the ground a bit. You'll need to continue to tighten your stabilizer jacks. I go round my camper every day when not on asphalt or concrete and tighten them.
Another thing, it sounds like you are not tightening your stabilizer jacks enough. You want your jacks to be as tight as you can get them, but not so much they lift the wheels off the ground. If you are not putting enough tension on them, well.... there is your problem.
I have no suggestions for the squeaking noise your experiencing. Something in the camper is flexing, causing the squeak. Maybe a shot of lubrication on your leaf spring joints may help the noise too.
Here's a little tip I learned a long time ago to get the stabilizer jacks nice and tight. After you have your camper level, crank the tongue jack down about 3 or 4 turns. If you have a power jacks, crank it down for about 2 seconds. Then, go the back of he camper and put your jacks down. Make them as tight as you can by hand. Then go back to the tongue jack and raise it back up those 3 or 4 turns, or let the electric one crank back up for those 2 seconds. This puts a little extra pressure on the back jacks, without over stressing them, or lifting the trailer. It makes the rear of the camper very solid. Then lower the front jacks nice and tight.
If you have tandem axles, folks testify the X-chocks between the tires are marvelous for removing trailer bounce too. I've never used them myself.
