Leveling pads/blocks while in storage

Thanks for the suggestion of cow mats, Ronfisherman. The local Tractor Supply's not all that local, but it turned out to be the only place around here I could get cow mats, in spite of the fact that dairy is still a significant part of agriculture in this area (I got a lot of "...um, cow mats?" when I called around looking for them). I did, however, locate horse stall mats at a ranch supply close to today's chore trips. These are a heavy rubber in various thicknesses (I got 3/4"), various sizes (4 by 6 feet is the smallest).

If I use wood blocks to level the RV, on top of these rubber mats, does the species matter? Redwood or cedar would be the durable choice, but will the tannins in the wood affect the tire rubber?