If you are actually using the camper over the snowy months, then by far, concrete is better.
Old house was on gravel and we used the camper throughout the winter. But shoveling snow off the gravel was not easy. No matter how hard I shoveled, it still left a bit on the gravel, and then it would melt (sunsine) and puddle and refreeze.
On asphalt (which would be comparable to concrete ... it's a solid surface), our current house is no problem. Of course I can use my snow blower and get all around the camper, there no danger of throwing rocks and once the snow is removed, the asphalt is dries in the sun. The asphalt is MUCH easier in the winter than the gravel ever was.
About the camper itself. I did not notice any difference where the camper was parked. There is such a space between the ground and the bottom of the camper, it doesn't make any difference. Air still blows under the camper. Neither gravel, stone, dirt, asphalt, or concrete retain enough heat (or cold) to make any noticeable difference with an object sitting 2 feet above it. In the summer, black asphalt will throw a lot of heat, but it doesn't throw any noticeable "cold". When it's freezing outside ... everything is cold!
If you do go with the crushed granite, I still suggest you put boards under the tires. This will raise the tire a bit and also keep water from puddling around the tire. Water won't hurt the tires, they are made to withstand the elements, but gives a good solid base for the tires.
More important than where you park (granite or concrete), is to keep your tires covered. UV sun rays will do more damage to the tires when a tire is not being flexed (driven) than anything else. I keep my tires covered when parked at home all the time.
If you have the choice, go with the concrete. And if you have snow, use store bought ice-melt for driveways or sidewalks. Don't use water softener salt or rock salt, or table salt. The salt will cause concrete to form pits, which are tiny holes. These tiny holes hold water. Water freezes, and those tiny pits begin to crack, making a bigger hole, or a bigger crack. Those hoses now hold more water, which freezes and causes larger cracks, and in a few years, a concrete pad has turned back into a gravel pad. Use the store bought ice-melt.
Good luck!
