My cat travels with me, but he HATES HATES HATES (reprint that 40x) a cat
carrier. Maybe your cats are mellow, John (they already get along with each
other the three of them?  then that's more than my cat with other felines),
but after getting Creamcicle into anything smaller than the van itself
(which he views as "the rolling cat box" and comes and goes freely when
we're parked on friends' land), he will SCREAM MEOW for HOURS ON END.  I
have found it best to just let him wander about the van while driving. I
notice he dislikes being in the back near the engine area while the van is
running (though that's where his food and litter are -- I have a GL with a
bed rigged in the center area, which is where he rides)...so maybe don't
place pet crates back there. Do your cats try to escape out windows at
traffic lights and rest stops? If not, I'd figure crating the dog would be
enough, and the cats will probably sleep on the bed with whoever is back
there.

YMMV
(Your Meowing May Vary)

--Patrice and "VanaBlue" 85GL