M.F.
Maybe start by having him potty with his shirt still on. My son (28 months) wants his underwear and pants completely off, but will keep his shirt on most of the time.
Also, kids are pretty good at adjusting to different situations. You should be able to explain to him that when you're not at home, he has to keep his shirt on for potty time. Maybe make practice outings to a friends house or to Target or something (for whatever reason, my son loves the Target family restroom and will use it every time we're in the store).
Also, you might want to let him practice dressing and undressing himself independently (if he can't already). When he has greater confidence in this area, he may feel better about keeping his clothes on.
As far as night time dryness, our pediatrician said she didn't completely expect it until age 4. Night time dryness actually has to do with levels of a certain hormone that shuts off urine production while you're asleep. The age kids are when that hormone reaches the right levels can vary. I know kids who wake up dry at age 22 months and others who couldn't do it until age 5.
Sounds like you're doing a great job so far!