Not sure where're your located, but Reading Truck Bodies out of Reading, PA is one manufacturer, Knapheide is another. Either one will have dealers thru out the US. Look in the yellow pages under "truck bodies". I'm sure there are dozens more.
I have a Reading 33" tall(above the bed rails) contractor style cap on my truck. It has one large swing up door on each side, no built-in tool boxes, and full height hinged doors on the back, no tailgate. This is the 4th truck I've had it on in 8 years. It has held up very well w/ the exception of a little rust on bottom of the back doors. I've repainted it to match each truck. These are heavy duty. About 500lb. The owner of the autobody shop that has painted them for me, groans when I come by w/ new truck. LOL
HTH.
Tom