For me 90-100% humidity is the norm. Band equipment being used outdoors, and even worse at the beach, will have tons of rust and worse. It may still work, but it will be ugly to the max. A cost of doing business on the beach I am afraid. I think if it still looks good, you should be alright. You will be rolling the dice on any cheap ugly stuff.

In my studio and in most studios I have been in, the equipment is always left on 24/7. It stays warm all the time and that helps to cut the humidity. Tape recorders, (Remember them?)will die quickly out in the humidity like being stored in a garage. All my master tapes have ruined in closets in my house. At least I was one of the first people in my area to buy a DAT recorder and then ASAP backed that up to hard drives. Real studios clean after every session and most of their stuff is near mint.