I just made 4 of these for the company truck. Without the tank top its just compartment storage. To use as a tank rack just set up to 6 tanks into the bin and slide on the top and you're good to go! Here are the pictures of the build:
https://www.facebook.com/media/set/?set=a.602557953211327.1073741854.179093372224456&type=1
https://www.facebook.com/media/set/?set=a.602557953211327.1073741854.179093372224456&type=1