A 26000 lb rated 5th wheel sliding hitch ??
The Curt slider up to 24k.
The Andersen system up to 24K.
A Reese slider up to 26k lb draw and 6500 lb load.
A B&W slider up to 20k lb draw and 4500 load.
A 26000 lb trailer is a bit much for light weight RV hitches and especially for a sliding hitch. It may have a 5500-6500 lb pin weight depending.
No doubt the 3500 DRW Mega cab can handle a GN trailer that size with ease as evident of the many commercial haulers using them. I see them with door numbers up to 38k-40k gross combined weights.
You might go with a custom haulers bed with say a light commercial hitch like the SAF-Holland FW001 that has a 8000 lb load and a 32000 lb draw rating.