If you need to raise the rear of the RV, use the tongue jack (for a TT) or the landing gear (for a 5th wheel) to do that. The blocks you linked to are used for side to side leveling, you only use them on one side of the RV.
For what its worth I have never needed more than one bag of blocks for leveling side to side. The tallest I have had to stack is 3 high. I just placed 2 blocks in front of that to build the ramp, used all 10 blocks that time.
With that said I do carry 3 bags of these things. I generally use the other 2 under the rear stabilizer jacks so they don't have to extend so far and are more stable.
EDIT: Looks like I was typing the same time Old Biscuit was :)