I have spent a fair amount of time in the Mineral King Valley, and as far as I know the only time my truck was bothered by any marmots was the time that I spent at least half an hour wrapping chicken wire around the truck, and wiring doubled up cardboard firewood boxes in each of the tire wells, and various other not so well thought out human obstructions for the marmots. And this was in the Sawtooth Trailhead parking area, as photographed by Shawn. When my wife and I returned from our dayhike to Timber Gap, a gang of marmots fled from beneath the chicken wire surrounding the truck. Upon close inspection, it was found that the complete underside of the truck hood had been trimmed of its furry insulating layer - seriously, maybe a few square inches remained untouched. A marmot had to be flushed out from its hiding spot in the wheel well, snuggled into an area between sheet metal and a rubber/plastic shroud. Once the truck was moved, it looked like a barber chair had been in that spot, from all of the dropped insulation that was chewed from beneath the hood. In probably at least 50 days and nights parked in the trailhead lots as well as camped at Cold Spring, that is the only marmot problem ever encountered.
One thing I have seen National Park Service forest crews do with their trucks, is wrap them like a burrito. Lay out a sturdy tarp on the ground, drive the vehicle on top and centered, then wrap up the sides and secure with rope. Usually, after June, it seems the majority of vehicles are left unprotected, and without problem.
I am not in a hurry, so don't be hasty.