Okay, I'm a bit confused. You mention flying to LAX, heading to Temecula, then heading west. I'll assume that you meant east since there isn't much more west to go. I've done the cross country drive twice (Seattle to Baltimore and Atlanta to Ontario). Just plain old driving would be about 5 days with 8 hours of driving a day. I don't know if the RVs have their speed governed like a moving truck does but I could not do more than 65 mph in the moving truck. Renting an SUV and staying overnight in hotels might be a better option.
Of course, what to see depends on the route you want to take. There's a myriad of ways that you can travel depending on whether you want to go north through NV/UT (I-15), northeastish into AZ (I-15/I-40), or straight east using I-10. You can hit up a number of National Parks on the way but I expect that their capacity is going to be limited at this time. I would also expect that a number of tourist attractions that require admission would likely still be closed or have reduced capacity. If I were driving at this time, I'd try to keep to natural attractions rather than things like amusement parks, and other tourist spots.