Replace RotoFlex with Pin Box That Stays Away From Bed Rails
Updated 12/03/2025 | Published 03/31/2021
Question:
I have a 2021 GMC 3500 HD Long bed truck with a Curt A20 hitch. I pull a Vanleigh Vilano 370GB 16K lbs..The pinbox that came with my RV is the Lippert Rota-Flex 18,K lbs. My hitch is set to its highest level. The RV sits level with 4 inch clearance from the truck bed. My problem is that beyond a 70 degrees turn of the pinbox, the plate that secures the pinbox to the RV starts to rub against the side of the pickup bed. I do have a tonneau cover, but even if that were removed there would be contact and I wouldnt be able to do a 90 degrees turn. I am looking for a pinbox that has a sharper incline going back from the pin that would clear my truck side. The Gen-Y 325-GH-8040 pinbox appears to have the clearance I need. Will the Gen-Y match up with the bolt patterns in the mounting plates on my RV? Is the Gen-Y considered a substitute for the Rota-Flex? I have the dimensions of the Gen-Y from another post, but it does not give me the height clearance underneath from the skid plate to the body of the pin box at various points.
asked by: Mike O
Expert Reply:
Most standard pin boxes will not make a 90 degree turn in anything less than an 8 foot truck bed, but that is due to being too close to the cab - not the rails.
You mentioned you wanted to replace the Rota-Flex with the Gen-Y hitch. Your old pin box and your new pin box must have to be the same bolt pattern (Like #1621) which dictates how big those mounting wings are. I don't think this is a solution to your need. This will just be another pin box that does not fit.
The best solution is a rotating pin box like the Reese # RP34FR "Sidewinder" style 5th Wheel King Pin that move the rotational point further back and keeps the pin box centered over the bed. Check out the video I attached that demonstrates the Sidewinder in turns.
This model works with pin box bolt patterns numbered 663, 665, 0719, 1621, and 1621HD. If you have a different bolt pattern number just let me know for an updated recommendation.
Now keep in mind, you will need a new 5th wheel hitch since the Curt A-series is no longer compatible with sidewinders such as the Reese # RP34FR. Instead, I recommend something like the Reese M5 5th Wheel Trailer Hitch - Single Jaw - 20,000 lbs # RP30928 with Wedge # RP44FR.
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on 5th Wheel Pin Box
Steven
12/3/2025
I have a Hummer H2 Sut, 34" bed, I have installed. BW universal rails. I have a CURT 24k 5th wheel Slider hitch at its highest setting. The Grad Design trailer has a CURT 20k Rota-Flex pinbox. OK, so I need 4" more height to clear the top of the bed sides by fractions. Also the length of the pin box needs to be longer by 12"-15" even with the slider. Please help.