Hardshell cases are the only way to go. In the mid 70s, I scored a bunch of Zero-Halliburton aluminum flight cases through the surplus channels for pennies on the dollar. They were deep-drawn aluminum, 26x26x16 for the hardware, and 4 26x26x36 cases for the drums themselves. Beautiful: 10 butterfly twistlock latches per case, and a gasketed seal at the lid. They were that very pretty NASA light blue, too. I made foam inserts for them so that everything had a place to go, and made little wood dollies with heavy casters for moving them (and speakers, and whatever else). In these cases, the gear can sit in the back of a truck in the rain and come out okay. I doubt that there are any of these exact cases are still out there, but mil-spec gear cases can be had through the surplus channels in any major metro area for very reasonable prices. Your tax dollars at work. I still have them: ought to shoot pictures of how they look many miles and years later. The gear inside is still fine, though!
Funny hard-case story one: the gasketed seal can be a lifesaver. I remember doing one booze cruise on Boston Harbor where things got a little rough, and my kick drum case got knocked overboard with my kick and the two rack toms (which live nested inside the kick) in it. Luckily, we were already tied up back at the dock, so all I had to do was grab a boat hook and retrieve it from the harbor: they float just fine.... And not a drop of water got in. With a soft case, I'd have been buying a bunch of new shells muy pronto.
Funny hard-case story two: having said that, mikeh is right. Trap cases are heavy, and having more than one can reduce the exposure to serious injury. If I had it to do again, I'd get two smaller ones, instead of the single larger one. We were loading out of a place called Chet's Last Call, the 2nd floor bar that used to be right across the street from the main entrance to North Station and the Boston Garden. The keyboard player was helping me get the 150+lb trap case down the fire escape to the truck, when a rather well endowed young thing decided to take an interest in him. So he let go to talk to her, and I ended up at the bottom of a flight of stairs with a beautiful, bulletproof, 150+lb Zero Halliburton case on top of me- and with a wrecked ACL and other damage to my right knee. My kick side, of course. That's when I started taking up other instruments, so I could play *something* while in plaster for the next 12 weeks. Twenty-plus years and three knee surgeries later, I still cuss that keyboard player on damp, cool mornings...