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Advisory on pickup box cross sill removal

The National Truck Equipment Association (NTEA) has issued an Upfitter Integration (UI) bulletin to advise of requirements to be followed when installing some fifthwheel- or gooseneck-style towing devices on a new GM C/K (GMT800) pickup truck with Fleetside box (RPO E63) with a fourth cross sill, used exclusively on the 3500 “Dooley” models.

Fifthwheel reinforcement crossmembers used by several towing device manufacturers require placement in the same location as the existing fourth cross sill. This is the number four pickup box floor reinforcement, located at the front of the box, and positioned just in front of the rear axle centerline.

Removal of the fourth cross sill is permitted with fifthwheel or gooseneck towing device installations only if the cross sill is replaced with a supporting structure of equal or greater strength to the removed cross sill.

Note that for pickup box corrosion protection, all paint damage must first be repaired and 2-mm-thick closed cell foam or urethane insulation material should be added between the hitch brace crossmembers and the pickup box floor.

For additional information on this advisory, upfitters, should phone the GM Upfitter Integration Engineering Assistance Line at 800-875-4742 or submit an inquiry on the UI web site,, by completing the Hotline Case Entry form on the site.

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