My son worked at Yosemite for 1 1/2 years so we have camped there a few times.
The 35 ft depth is for your camper AND you car/truck. Many sites in Yosemite are very tight with big trees so you should abide by the recommendation. The campground roads are tight too so if you try to put your 26-foot trailer in and your car, you may be sticking 2 feet into the road which will impede other campers.
If you are trying to make a reservation for the summer, you MUST get onto the website as soon as the sites becomes available (I think 5 months before the date). One time I was trying to get July reservations and the campgrounds filled up in 11 minutes!
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
RVing for 19 years & 150,000+ miles