I used a bus when I did RAIN a few years back, tho' I'm not sure it's the same one. I'm on my own so it was a good option. I wasn't racing - I finished 300th - so the bus was at the rest stops when I got to the rest stops, and it was really nice to be able to get to stuff I didn't want to carry (like extra sunscreen) and yea, use the potty without waiting. We also chipped in for a cooler of stuff so that at the end waiting for everybody we could just chill under a tree. Of course, we had to wait for the last person - but we could rest. I had a two-hour drive home afterward but that wasn't so bad (I stayed in the Hampton before the ride, though).
Oh... I do remember that the bus guy didn't care for non-standard-shaped bikes... didn't like them thar recumbents at all!