I make sure we bath instead of shower. We never touch it (or try to pull the foreskin back) and I put whatever potion or lotion or cream I have around on it. Sudocrem, moogoo, oatmeal cream. Whatever is some kind of soothing treatment.
Also, I try to encourage him to not leak wee. I don't know if this makes a difference, but he's a bit lazy some days and doesn't wee when he needs to and lets little bits come out. I don't know if it makes a difference, but being warm and wet with urine all day can't help.