Here you go, some reading for a couple of days!
SELECT DESIGN does beds, interior and exterior upgrades to F350-F550 trucks.
ACCUBUILT sets up F450 and F550 trucks and has a pickup appearance instead of an aftermarket specialty bed. There is not a lot of detail on their site as to what they upgrade but if you are looking for a pickup on steroids this would be one place to start.
SHIP-THRU UPFITTERS
Fontaine = Fontaine Classic Traveler tow body by Fontaine Modification. Looks sorta like a Dooley pickup, only better.
Manning Hauler = Manning is right outside the KTP truck plant, and their motto is "When was the last time you got mad at yourself for buying the best." The Hauler is a nice tow body, and Manning will instead mount a plain ole Dooley pickup bed on a chassis cab.
Monroe Versa-Hauler = Monroe is in WI. Scroll down to the "Ford F550 Crew Cab with Versa-Hauler Towing Body and Optional Trim Kit, Running Boards, Wheel Simulators and Sun Visor." Also note that Monroe will mount other types of tow bodies and flat beds on your rig.
Knapheide = a famous service body outfit also makes the Knapheide Westerner Storage Body, which provides safe secure storage plus towing ability in a low-profile body. If I were designing a tow body, this would be very close to perfect if you have payload capacity for a heavy steel body. Knapheid also has a Westerner flatbed gooseneck hauler.
Knapheide also has several distrubutors that are also Ford ship-thru upfitters:
Auto Safety House in Arizona.
Carter Industries in California.
Dealer's Truck Equipment Co. in Louisana, Oklahoma, Arkansas, and Texas
Frontier Truck near Denver.
Layton Truck Equipment in Colorado, Indiana, and Illinois.
Unicell Body Co. in western New York.
A.E. Truck Equipment = They have "trailer towing bodies"
Rough Rider = Harbor Truck Bodies in CA offers a plain flatbed gooseneck hauler.
Badger = Hoekstra in Michigan will mount you a heavy-duty flatbed gooseneck hauler with side boxes, the Badger by Omaha Standard. Look under "Platform and Stake bodies".
Reading Redi-Dek = Reading is a famous service body maker that also has a neat flatbed gooseneck hauler with under-deck storage boxes. Look under "platform bodies".
Other ship-thru upfitters that will install a Reading Redi-Dek:
Brake & Clutch, Inc. in Salem, MA.
Rayside Truck and Trailer in south Florida.
---------end of Reading upfitters
Most upfitters that will install a flat bed or platform body will also add a gooseneck or fifth-wheel hitch and side boxes. So you might want to check out the following Ford ship-thru upfitters who have flat beds or platform bodies or stake bodies, but don't mention on their website that they'll customize them into towing machines:
American Cargo in Indiana.
America's Body Company with plants in OH, LA, CA, MD, PA, NJ, MO, MI, KY, and OR.
Dejana Truck in NY, RI and MD.
SIA Truck Bodies with several locations in Florida and Alabama.
General Truck Body in Houston.
NBC Truck Equipment in Washington state.
Scelzi Enterprises in Fresno, CA.
Stahl Div., Scott Fetzer Co. = Stahl is a famous maker of service bodies and flat beds, and is a Ford ship-thru upfitter. They don't make tow bodies, as far as I can tell.
Supreme Corporation is one of the big boys you've heard of, with plants in IN, NC, GA, TX,CA, PA, FL and CO.
OTHERS:
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Most of these will accept a new truck drop-shipped from the factory, and fix it up to your specs.
Highwayman = tow body by Highway Products (800 ToolBox)
J-Rod offers bodies, tool boxes and trailers
Western Hauler = Western Hauler tow body in Fort Worth
Classy Chassis = they have new trucks ready to go, or you can drop-ship your new Ford to them and they will fix it up exactly like you want it.
Gooseneck = The original Gooseneck company also makes aluminum tow bodies
Douglass = Douglass Truck Bodies 5th-wheel tow bodies
Centurion = Centurion conversion adds a factory pickup bed to chassis cabs.
J&J Hauler = J&J Enterprizes hauler bed on F-550
Herrin Haulers = several styles made in Kilgore, TX
AACSON = nice aluminum flatbed/gooseneck hauler made in western Canada
B&W Custom Truck Bodies = nice tow bodies. Be sure to look at the Elite tow body. These are the same folks that make the B&W Turnover Ball gooseneck ball mount.
Boden Fabricating = Smokey, please ad to your list the fine folks at BODEN FABRICATING in Edmonton, Alberta. Talk to Ab Deacon..........these folks make EXCELLENT tow bodies, welding decks, and service beds. SM Tatham
2L Custom Trucks = has nice tow bodies. hhroper added this one to the list. Looks good!
Suspension Control = Their new website explains that they do more than suspension. They have nice tow bodies.
Utility Bodywerks = see the feature article about "Light Medium Duty Trucks" in the feature articles section off the "contents" button on the menu bar at the top of page 1 of this thread.
Intercontinental = An oufit in MT that will mount you a lightweight aluminum flatbed with an optional fifth wheel hitch.
Mountain Master = makes a heavy-duty tow body in Phoenix.
Roll-a-long pickup beds and tow bodies for chassis cabs.
New Haven Body for those folks in New England that want a local upfitter.
FarmBro is an upfitter in eastern Canada that does Fontaine conversions and other work. See post from wandrr below.
Godwin is a big outfit for folks "back east". nc_stroker says you should check them out. They will make you anything you can dream up - not just the standard stuff on their website.
Trail-Hauler makes hauler bodies in Tennessee.
Tuscany makes hauler conversions in Elkhart, Indiana.
Truckcraft has aluminum flatbeds/platform bodies with optional gooseneck balls or fifth-wheel hitches and storage bins. Made in Pennsylvania, with dealers throughout the U.S.A. and Canada.
Select Solutions in AZ converts F-Series trucks into Select Design trailer toters.
CHARIOT Hauler Division aluminum body with a few upgrades and accessories available.
Sorry the links didn't come across, so just do a search for the names.
Good luck,