T.H.
That sounds like a long trip! I wouldn't worry too much about the little guy. At that age it's pretty easy to travel b/c they really will sleep most of the way. I'm not a huge fan of getting in the back seat with my kids during road trips, but on such a long trip you maybe want to consider doing it for a couple of the stints in between feedings. I wouldn't sit back there the whole time, but since he's so little and rear facing you may want to consider sitting there for a just a bit to play with him during his normal awake time so he doesn't sleep the entire time and then stay up all night.
Other than that, I'd say plan on taking your swimming suits and swim as much as possible in the hotel pool to wear out your 2.5 y/o. If possible, I'd even swim for an hour or so BEFORE you leave the hotel in the morning so it increases the likelyhood of him sleeping while on the road!
Good luck!