You (the OP) didn't say how big (long) your Class C is. From what I've read in these forums, a Class C with long rear overhang can often feel squirrelly in it's steering. Also, correct alignment of the front suspension for a loaded Class C motorhome is VERY IMPORTANT to proper steering.
I put Michelin LTX M/S2 215/85R16 tires on my short Class C a couple of years ago and they are handling and riding just great. I stayed away from Michelin RIB tires because of their pure highway tread design, as I wanted the more aggressive Mud & Snow design for best all around traction. I use 80 lbs. in the rear and 65 lbs. in the front on our 24 foot E450 Class C. Our E450 chassis came with a steering damper shock, which may be helping.