1

Just for the record we are renting a 22 ft Class C motorhome.

2

Drive the Tioga Road. Much better.

3

Just drive slowly. It is now two-ways with one lane on each side, not two-ways on a single lane around a bend! There is no guardrail, as you probably already know.

Unless there have been changes, I don't think that there is RV overnight parking in a campground in Mammoth. I think that there is a primitive campground along Highway #395 nearby a hot springs. I have not been there for a while. I did not stop in 2008. LeeVining also does not have a campground.

4

Just for the record, California and Vegas are not referred to as the southwest.
More like Arizona, New Mexico and west Texas.
No problems driving Tioga Road except slowing down the frustrated cars behind you.
You may want to park the rv in Yosemite Valley and take the free bus around.
You will see more and enjoy it more. Parking gets nuts in the summer.

5

Many people do that drive in an RV (it's no coincidence that there's a line of RVs called "Tioga". The grade east of Tioga Pass is extremely steep, though, so let your brakes rest by shifting to a lower gear and pulling off the road at turnouts. Indeed, it's the law in California that slow moving vehicles on 2-lane roads need to use turnouts to let cars behind them pass.

6

You can preview the drive down Tioga Road here: http://www.youtube.com/watch?v=q28OGoegxIE The drive starts about a half-mile east of Ellery Lake.

If you are referring to Highways 190 or 155 to cross the mountains, they don't look like real good options to me, not in an RV anyway, but I haven't driven them, so I'm not sure. I looked for some vids for there, but couldn't really find any.

Your best option if you don't want to take Tioga Pass is to continue south to Bakersfield and take Highway 58 through Tehachapi to the Mojave Desert, but then you miss all the lovely scenery on the east side of the Sierras. Here is a time-lapse vid of that drive: http://www.youtube.com/watch?v=SNGh_uueOGs Too bad this guy didn't clean his windshield before he filmed. Check out the semi cutting him off at 4:11 and the windmills as they come into view at the pass around 6:00.

7

I've taken both Hwy 155 and 190 on a motorcycle. They are highly challenging on a sportbike; they'd be impossible in an RV. Neither cross the Sierras anyway, but I wouldn't recommend them as a "shortcut" on the western slope either. Hwy. 178 is the most scenic route through the southern Sierras that can fit an RV.