Call directly to the manufacturer of the Tri-glide.
They usually have different lengths of pinboxes, that fit the same framing.
About 2 years ago, we got a bunch of new Cardinals in with Roto-flex pinboxes. When we put them onto short bed Chevy trucks, they would hit the tailgate and tear the truck up. Forest River paid the damage, and swapped out the pinboxes for shorter ones....
Steve and Vicki
2011 Dodge 3500 CTD Outdoorsman
2013 Columbus 320RS-ITS HERE!!