This afternoon I put my fiance's RV up on blocks to reduce wear on the tires, and it wasn't as hard as I'd feared. Just in case anyone else out there ever has to do something similar, here are the steps I followed -- but be careful! I figured all this out for myself, so your mileage may vary.
First, I went on eBay and bought a couple of maintenance books for the old Dodge van chassis that the RV was built around. They only cost a few dollars each, and from them I was able to identify the lift points that are safe to use when jacking up the vehicle.
The front was easy to jack up because the lift point was right in the center between the front wheels. I just stuck a Husky 6-ton Bottle Jack under it and pumped it up. I didn't take the tires completely off the ground, as the picture below shows, but I did take most of the weight off them.
As you can see, I used a pair of 11.5-inch cement pier anchors for the blocks with a couple of pieces of wood and cardboard on top to level them out.
The back was more difficult because there isn't a central jack point -- each side had to be lifted seperately. What's more, I had to crawl way under the vehicle to position the jack and then the blocks. As you can see, there were lots of spiderwebs, but I didn't see any spiders. The webs were old, and I doubt there were any spiders around anymore since we put an Ultrasonic Bug Repeller in the RV.
Anyway, you can see the 10-inch blocks I used under the rear axles. I decided to position them beneath the spring U-bolts; it's not a great spot, but it's the best that was available. My main concern is that the weight is resting on the bolts, but nothing else was possible. The wheels are still bearing some of the weight, so it should be ok.
And that's all there is to it!