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Determining Which Reese Goose Box Will Fit 2021 Aliance 370FB 5th Wheel Trailer


Will this gooseneck RP94720 fit on a 2021 Alliance 370FB . I have 2021 GMC 3500 standard bed and like to get a full 90 degree and this look like the best thing to have..


Expert Reply:

I would be happy help you determine the correct Reese Goose Box for your 2021 Alliance 370FB, but you will need to find the model of your current pin box first.

To do this you will need to find the white sticker on your pin box that has a four digit number like 1621 or 1116. If you cannot find the sticker just send me a picture of the serial number on your pin box and I would be happy to identify it for you.

The Reese Goose Box 5th-Wheel-to-Gooseneck Air Ride Coupler Adapter - Lippert 1621 and 0719 - 20,000 lbs # RP94720 you were looking at is confirmed to replace the Lippert 1621 or Lippert 0719 pin boxes so if this is what is on your trailer it would be an exact replacement.

If you have a different model pin box just let me know.

Now regarding getting a full 90 degree turning radius, the Reese Goose Box does not have an offset so since your 2021 GMC Sierra 3500 with the OEM prep package has the 6-3/4' bed this still may not allow that unless your trailer has a tapered nose.

The best option to get the most turning clearance on a truck with a bed shorter than 8' is going with a rotating pin box like the Reese Sidewinder 5th Wheel King Pin with Rotating Turret - 20,000 lbs # RP34FR which moves the pivot point of the trailer from the king pin to the turret which gives you 22" of clearance.

With a rotating pin box you will need to use a fixed hitch like the B&W Companion OEM 5th Wheel Hitch for Chevy/GMC Towing Prep Package - Dual Jaw - 20,000 lbs # BWRVK3710 which will fit directly into the puck system in your truck so you will not need an adapter.

In addition you will need wedge # SWW-06 to keep the king pin from rotating in the hitch.

If you can confirm which pin box you trailer has I would be happy to go over the exact pin box options for you.

I included videos of the products mentioned for you to take a look at.

expert reply by:
Samuel C

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