Yep, with GMs you need interface box to fake out the IBC into thinking it's talking to standard electric brakes. Had one with our '05 and now with the '11.
You might check with your dealer of the RV MFR, some such as Redwood include the interface box as part of the Disk Brake package.
2018 Chevy 3500HD High Country Crew Cab DRW, D/A, 2016 Redwood 39MB, Dual AC, Fireplace, Sleep #Bed, Auto Sat Dish, Stack Washer/Dryer, Auto Level Sys, Disk Brakes, Onan Gen, 17.5" "H" tires, MORryde Pin & IS, Comfort Ride, Dual Awnings, Full Body Paint