Keep gear secure and easy to reach with under seat storage set up as a rear cargo area organizer. If you want it to stay put, consider a mounting bracket that supports the box when partially pulled out, or plan solid tie-down points. Wheels make moving a loaded container simple, but compare inside and outside dimensions to your space so it fits without shifting.
Yes, a bracket with a sliding track lets you pull it out partway for access. The bracket supports the box when partially pulled out. If it's in a truck bed, you can slide it toward the tailgate and rotate it onto the tailgate to open the lid.
Add a mounting bracket to attach it so it stays put and still slides on a track when needed. In a truck bed, strap it to D-rings or let the wheels sit in the front-to-rear bed channels to reduce side-to-side shift. In an SUV, apply sticky no-move carpet rounds thick enough to clear the wheels.
Look for tough plastic with metal hinges and closures plus 3 lockable snaps; a metal rod across all 3 snaps can lock at one end. Some include 4 gun slots with a rubber interface and Velcro ties. If ties don't hold well, use zip ties and consider adding egg crate foam to the top and bottom for extra protection.
Wheels make maneuvering easier, but a mounting bracket will keep it stationary. In a truck bed, the wheels can sit in the bed's channels to help prevent side-to-side shift. In an SUV, add sticky no-move carpet rounds under it to limit rolling during travel.