I have never bathed Caleb...he might get a bath this summer, if the drought warnings and water restrictions are lifted.
As far as keeping horses clean, I cannot advocate enough the benefit of corn starch. Perfectly natural, easy to use and the more you use it, the better it works. It really helps if you put it on before a ride, and brush it out after.
If you have access to hot water, hot toweling is a good option if there's not enough time for a full bath, or the weather is too cold. Also an excellent option for horses who are afraid of hoses.
Also baby powder is wonderful for drying up sweat and keeping saddle pads, girths and whatever else fresh. I go through it like a baby drinks milk. I even use it in my hair on hot days after rides, probably looks a little funny, but it feels nice after wearing a stuffy helmet for 2+ hours.
Oh and grape-seed oil is a wonderful, wonderful, help for dry, flaky skin/hair and it's very light and easy to rub in, so it doesn't attract a lot of dirt compared to other types.