Get there early on your day of your arrival and you should be fine.
Remember, half of Tuolumne Meadows Campground campsites are first come/first served, so if you arrive early I'm very confident they'll be able to assign you a campsite that will fit your RV. Unlike at other campgrounds in Yosemite that accept advance reservations, one is not assigned a specific campsite at Tuolumne Meadows until one arrives at the campground.
Try to show up there by 10 AM and you should be fine. (You'll probably be fine if you show up by 1 PM too.)
The worst case scenario would be, as you already mentioned, that you'll need to park your truck in the overflow lot. But again, with only a two-foot difference in length of your RV and what you reserved, I doubt that will occur. But to be safe, arrive early at the campground.
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Edited 1 time(s). Last edit at 03/15/2014 06:02PM by plawrence.