Considering renting an RV in LA to spend some time in Yosemite in March 09. Any suggestions?

So before you get the cart before the horse, here are a few items you need to get straightened out before you go too much further down the planning path you're on. The first assumption is that there is some generic 'RV'. In point of fact there are three basic classes, simply enough: A, B and C, so before anything else you should have a look at those and see what appeals to you, and what you can handle.

A Class B or C motorhome would likely be something you could handle and also be very likely to have an automatic transmission. Still, it will almost assuredly be significantly larger than what you are used to driving and will require some getting used to, at the same time you're trying to get used to being on the 'wrong' side of the road. Also keep in mind that they have limited visibility at a time when you may not be looking in the right direction.

The second assumption is that an RV will "save money and time". That is not a given at all. You will need to look into what one actually costs to rent versus a standard sedan and motel rooms.