Thought I had some pics but I don't .  '01 F 450 crew cab 4x4 7.3L.  Has a tool bed on it.  I thing in between it's 11'x about 4' .  Only reason we bought it was it was dirt cheap and only had 80,000 miles on it a couple years ago.  It belonged to a lease company, case IH leased it and the company didn't want it back, so they sold it for a little more than the taxes on it.  Didn't think we really needed a tool truck, but the thing has already paid for itself saving trips back to the shop for tools.  It's also nice since theirs 6 of us, we can at least haul 5 to the field in it if we need too.  We haven't put a compressor or anything like that in it yet, may just get a roll around to put in it, we only need it  a couple months in the spring and a few in the fall, then it would only be occasional since the battery tools are pretty powerful now. 

Never did it. Never seen it done. But I've always wondered if it would not be a good idea to have a service trailer instead of a service truck. Most farms have multiple pickups, trucks, tractors, etc. Why not put all that service stuff on a trailer that could be pulled with whatever was handy at the time? Maybe someone has tried this and it didn't work?