I found one of these types that fit in my TJs. I holds a ton of ****! We beat on our Jeeps and there is some tricks to learn on keeping tools and such from rattling. Old towels and pack it tight helps.
I built a box out of 1" plywood. Brackets on the inside. 4 holes in the bottom with j hooks that secured the whole thing to the floor. Back end of the top follows the outline of the inside of the tail gate. Back end of the bottom stops before it gets to the tire changing stuff. Painted it but mine is never outside in the rain with the top down. I put 4 large eyehooks on the outside top corners so I could strap more stuff down if necessary. 2 door Jeep so no back seat of course.