The parking brake is really the #1 feature of the drum brakes. The disc-based parking brakes are less reliable. At minimum, you have to use it fairly often.
I worried about this problem for a while and then realized that over the years I had owned the truck, I had never used the parking brake (although it did work). Using one to stop a vehicle is a risky proposition and that's not what its there for. This is why the manufacturers call it "parking brake". It's for legal reasons, just like how the "firewall" is now called "front-of-dash".
With an automatic, you put stress on the parking pawl to use it on a hill, but you have the mechanical advantage of the differential to help. If you really need holding power, lock the front hubs and shift to 4LO. This gives additional mechanical advantage and spreads the force out. Even if a driveshaft breaks while you are parked (which seems really unlikely), the other end of the vehicle still holds.