I too live where it is hot so I have one small unopened vulcanizer tube in my saddle bag and one larger opened one at home. If kept at home and sealed tightly it can last a long time.
The only time a vulcanized patch (that is what I am calling them now) doesn't work if one doesn't wait long enough for it to dry before applying patch. i was surprized to see the Rema instructions say to wait 5min to dry. I usually one wait ~2min.