FIRE!! 48 GMC Panel bed caught fire!

[BBEEP]

So, this is going to be a 're'build thread soon, I guess. I have driven this truck for years, towing cars on my trailer & generally having fun. Last Thursday I towed my Impala to Salem, Oregon (about an hour). When I took the exit, I noticed smoke in the back--inside. I pulled of the road, thinking that a tire was rubbing, or a brake was locked up. Unable to determine the problem, I parked the truck, unloaded the car from the trailer and continued on the other 2-3 miles. An hour or so later I came back with my friends pickup, loaded my Panel on my trailer (no smoke), and towed it to the fairgrounds where my Impala was.
As I walked by the trailer, I noticed smoke coming out the drivers window!! (I never tow with a window down, thankfully I did this time) Upon opening the back door I saw one foot flames in the middle of the floor!!! Thankfully there was an extinguisher in my truck and I got the fire out soon.
This is an early Panel, and as such, it has the wood planks with metal strips like a pickup as opposed to plywood used in the later models. I need to let the insurance adjuster know what is involved in replacing the wood.
So here are the questions: Is it wider or longer than a shortbed 1/2 ton?
And is it like a pickup, where you have to remove the bed for install? When I removed the plywood floor from my 52 Burb, it was under the body. Do I have to lift the body of the Panel?

HELP!!