Aw shit was that me? I think there's a few of us postal comrades on here.
The first 90 will be rough no matter what you are going into, you will be expected to put up with a lot of shenanigans. Use that time to figure out who the shop steward is and see what they're pulling on you that is not actually by the book so you're ready to grieve and protect yourself once you're not on probation.
I work inside so I don't know what the most current tech is as far as keeping cool in summer but I'm sure your coworkers will have good suggestions.