I just installed four boxes similar to the ones you linked to, except they are only 36 inches long. I intend to use them for the propane tanks supplying the range and water heater, and fuel tanks for diesel heaters. Mine are between the axels to better protect them. Here is my YouTube video showing the installation process:
I love how they turned out. Way prettier than anything I could have fabricated. I got them on sale, so the four boxes and related hardware came to under $1,000 Canadian.