As much as I dislike using plastic of any kind for anything in your case living in Florida an all I would suggest going with a high density polyethylene plate but it's gonna be dear and never having used the stuff myself I don't know how it will stand up to shop abuse in the long run.
I understand what you are saying about humidity, I live almost straight north of you, ok it's a long way north up in Manitoba Canada but it's still north. As strange as it sounds the lowest the humidity has been here since Dec.1 is 87% this is very strange as the normal winter humidity is somewhere around 24%. This is a huge problem for the cabinet shops in the area as anything built here this winter is going to shrink.
Retirement is easy, but You really have to work at it.