DO NOT get into the bus only or transit lanes, the cops will give you a ticket in Las Vegas. My wife saw several cars getting tickets for stopping in the wrong lanes.
My suggestion is also to go to the car rental site. You will want to check it out in advance (think really early in the morning - before 8 am? when it is just light enough to see around. Then go back when they arrive at the rental area. There is a "Tiny" parking area for private cars across from where the rental car counters are located, and where the bus drops off passengers. As I recall, it is about 40 parking places for small cars, nothing for a RV. By you can drive through the lane, stop for a minute, pick them up, and keep going.
They will just need to get their baggage, then take the shuttle bus to the rental counter. From bagage pickup, you cross the street to the shuttle pick up area. Then they drive you about 2 miles south to the rental car area. I would suggest checking it all out on Google.maps.com and then find the airport, rental car area, and then click to 'earth'. This will give you a overhead picture of the parking area, ect.
My wife made it to the hotel much faster than the rest of us. We went to the rental car area, then stood in line for 60 minutes, rented a car, went downstairs to pick one out (cars had the keys in them, you just get into the correct size and color of your pick). Then waited 45 more minutes to get out of the parking garage! What a PITA. . . She took a $12 per person shuttle bus with a wheelchair lift. It goes up the strip and stops at around 10 places, then our hotel on the south end of the strip. She boarded very close to the free shuttle to the rental car area.
Anyway I would avoid taking the RV to the airport. The car rental area will be OK. Just make sure they are there, or on the bus to there before you start into the parking area of the rental car, as you will not be allowed to park there with a class A.
Good luck,
Fred.
