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If you are concerned about the integrity of a shell and not concerned about weight then you may want to check out Caravan Camper Tops. Steel frame and steel cover. Solid construction made in Reno, NV. Very secure. I had one previously on my Dodge Cummins 2500. Go to:
http://www.caravancamper.com/
From their Homepage:
An All-Purpose Truck Canopy | Built to Order
Built to order in two basic models...you can use this top for hunting, fishing, camping and prospecting trips. It is an ideal truck top for commerical use. Sealed weather-tight, it will protect the load you wish to carry in any kind of weather. Made with a rigid steel frame, covered with Paintlock steel, you can carry your load on top boats, luggage, pipe, lumber, etc*. No extra charge for installs at our plant.
Caravan Campers can be built for ANY size pickup!
Rigid steel frame-heavy angle and channel iron, continuous channel iron bracing
Covered with 24 gauge Paintlock Galvanized steel
* Will carry maximum weight on top (shell equipped with racks), up to 2000lbs spread evenly without injury to camper
Strong enough to handle mountain roads and Jeep trails
Doors are double wall steel with heavy duty hinges and lock hardware, vertically hinged eliminates reaching over and climbing over the tailgate
All sliding side and front windows are heavy framed Motor-Home quality available in tinted or clear tempered glass
Optional pressurizing air vent is water resistant and increases the inside air pressure which keeps DUST OUT!
No additional cost for installation at our plant.
All Caravan Tops are dust and water resistant. Where metal meets metal, we seal with heavy sponge rubber.
I'll be watching your build with interest. Waiting to see the 2018 model year F250 4x4 Powerstroke. After towing with the Adaptive cruise I am hoping that the aftermarket bumper issue will be solved because the adaptive cruise really works well towing long distances.
Tad