It is very common to have one underbed box mounted near the cab on a flatbed, but take a look at this approach. Here is a series of underbed boxes of varying sizes that are connected with a wheel skirt insert making it look like it is not a flatbed at all, but something else. In this case, the bed is a 14' stakebed from Harbor Truck Bodies in Brea, CA. Just think of all the stuff you can put in all those compartments which are 18" deep! Then do it again on the other side. What a great way to be able to carry things that are kept out of sight and out of the weather while doing the things you need to do with the stakebed. A great combination!
Let us build one for you!