When additional help is need to get the MH level ( so wheels aren't off the ground by using hydraulic jacks), would it be advisable to support both rear wheels? If you used blocks under one wheel the...
If you can use enough lumber to support both tires, then you definitely should. But, if you don't have boards big enough, then supporting only one tire will work. After all, the tires are rated for "X" weight, but also have to tolerate bumps, curbs, etc while rolling. When on your supports, the tire is static and one tire can easily handle the load by itself. Also, you are probably only going to park there for a few days, not months.