I have a 36 ft. motorhome with exhaust brake and have been driving many years both m/h and truck and I can't find where it is said that using the exhaust brake in bad weather can not be used...any he...
"Bad weather" can be subjective. I wouldn't use my exhaust brake on icy roads, because letting off the throttle could cause the rig to skid when the exhaust brake engaged. But slightly wet roads, at reasonable speeds, is a different matter. YMMV