Topic wise, I think stashing the extra CV axle (or 2) under there is a fantastic idea!. The things weight a ton and take up way too much space in the vehicle, plus, if you don't lash them down securely enough, they could become deadly. A purpose built water resistant case of some sort would be the ticket. I'm doing it! Thanks for the idea Patineto!
Coming from the world of "do anything" motorcycles, you get used to strapping stuff all over you bike and use whatever space is available..
Yes lower center of gravity need to be address and the laws of provability as well as Murphy's law..
Looking under the truck is so much space under, in between the rails, actually i'm surprise nobody offers "drop down boxes" for the sliders, they don't need to be big or stick down, but hey 5 inches is more than NO inches
Personally I will not go any farther than a pelican case, bulletproof stuff, just don't drill it out, much to cheesy, think of it as a challenge.
Can you imagine 4 palican;s of the exact same size, one on each color so you can identified them at a glance, man I'm going to steal my own idea....
Other tip..
Bicycle toe straps are a fantastic way to strap small things, very dependable and easy to release..
Many moto guys use Zipties, man they poke so hard when you hands are wet, then you need a way to cut them and have spares to reinstall whatever you took, toe straps will last for years and they are cheap since most people ride clipless.
Look for Nylon straps with a nice "Head"
