In-bed tool box

Hello. I read another thread with this exact title. But it was a bed rail tool box. I need to know what you use, if I'm mounting one on the floor of the bed between the wheel wells of a double cab 16' taco. I'm willing to drill through the bed. Do I need special washers to keep the plastic from wearing out, or is the plastic pretty strong?

 

The plastic is a fiber reinforced composite that is pretty damn strong. but washers will definitely help spread the load and keep bolts/nuts from pulling through if you drill it out, just a matter of contact area. Same would go if it was a steel bed since most bolt holes are almost always oversized.

 

Thanks. I'll use some nuts, fender washers, and 3/8 all-thread rod, then. A pair on both sides.