Depending on where you live,there should be a truck body manufacturing/installation outfit/company in your nearby area.
Supreme is in central PA and somewhere on the West coast.
Mickey bodies are in the Carolinas.
Knapheide makes stake and flatbeds.
Reading makes utility bodies.
Do an internet search on truck bodies.
There are a ton of listings.
You may even find a less expensive used body.
I had Supreme do the 14' box on my Mitsubishi Fuso 4X4 (FG-639) a few years back.