I thought I'd post a recent experience as 120 via Yosemite isn't driveable without getting a ticket for entry. These tickets are impossible to get due to bad website design and limited number. Until CV19 goes away this will be the case
CA108 doesn't allow any RV over 40ft. For a small portion there's a limit of 30ft. The road has been improved over the years, thus some of issues people remember aren't the case anymore. Ie there's no one lan segments, while not hugely wide, it's wide enough for RV and other vehicles to pass in opposite directions.
The portion of 108 west of the pass really isn't an issue. The western side I never needed to move out of drive. In fact this fools a lot of people into thinking they'll have no issue on 108. The problem is the portion east of the pass. This is where you will find 26° hairpin turns, with very short switchbacks. If going east to west, you'll need to be in 1 for a good portion of eastern side. Even then you're likely to only be going five-ten mph. Going west, to east, you'll want to be in 1 for engine breaking.
I've driven it in a 25-27ft Class C. Anything bigger/heavier will have problems on the eastern side of pass. However anything under 25ft-27ft is doable. I wouldn't recommend a class A. Mainly cause they normally have lower ground clearance, and are generally longer and heavier.
However don't be afraid as long as you're within those limits. I won't pretend it'll be the easiest drive. Slow and steady wins the race here. The biggest danger during my last two crossings, cars/trucks speeding around corner over the centerline.