I had a 1988 Bounder on a Chevy P32 chassis. The factory tires on it were 8R19.5. I changed to the 225/70R19.5 tires on the front but kept the 8R19.5 highway tires on the rear. I too go off road. I never worried about bashing the engine or transmission pans. The motorhome set down over the frame such that the motorhome body would get whacked before the drivetrain stuff. I only bashed the body once!
Have you had it into the locations you wish to take it? If so how was your traction. I found that I had excellent traction. My favorite spot is 1O miles of dirt (not gravel) road off the pavement. On two occasions while I was towing my Jeep there was enough rain that the top 3" of the road was mud. This road has several grades of about 10% for short distances and was curvy and rough enough the 15 MPH was about the top speed I could go. The driver tires slipped a little a few times but I never had problems.
I also drove Monarch pass in a early 6" snow storm before the snow plows got there. I once drove towing the Jeep from Mammoth Hot Springs Yellowstone National Park to Sheridan, WY via I90 in an almost blizzard. There were cars and SUV's all over the ditches and I never spun a wheel.
What I'm trying to say is you may have plenty of traction with highway tires. Motorhomes put a large percentage of their weight on the drive axle. Maybe that is enough.
Whatever you decide good luck. I looked around and other sources for the traction tire in 8R19.5. Here are a couple places at a far less price: SpeedyTire
Hopefully they actually have tires...not just a good price for tires that are out of stock!