brp,
Interesting wheels and tires. I love the look of your set up with 40's. That is great for a no-lift truck. Ford is certainly the best of the bunch for tire enlargement with Dodge at dead bottom, clearance-wise.
Now you say you want to install a 75" wide camper? That is very narrow. I have a Lance Lite 165-s (similar, but older version of the 825) that is 86" wide, outside to outside and I thought that was as narrow as a full service hardside gets.
The solution for the 35 spline Dana 80 FF rear axle on my '01.5 Dodge CTD 2500 was to buy Mickey Thompson 12" wide x 16" aluminum wheels (with 4.5" backspacing) to replace the 7.5" wide, 6.5" backspacing stockers. The tires are 33/15.50's and are considered super singles or duplex and take the place of duals. However, the load rating is only 3750 pounds, so it won't carry the water in your tank. I have 10" wide front wheels with 33/14.50's with a 4.5" backspacing but they stick out so far they hit the rear of the fender opening on full turn. So, for the moment i'm using the stock front wheels with 33/13.50 Tactical tires. The solution may come from a Mil. surplus tire/wheel dealer who has hundreds of 80% tread cast-off Hummer wheels and tires. The wheels are 8 lug (to start) and will fit the Dodge. The difference is the 7 inch back spacing. I don't know if they will fit. The tires are 37" tires which actually measure 34", a good height for my rig's lack of clearance. The problem is the lower door hinge protrudes into the fender opening with a little bump in fender metal.
So to the question. With that set up, I'm about 8" narrower, outside to outside compared to a stock dual set up. I put 7" wide Jeep TJ fender lips on the rear to act as hips. The camper is very stable when on the truck with super singles. Here's a pic:
I hogged out part of the front bumper and fender and added wide lips to deflect the mortal enemy of my Lance, wooden frame TC: water intrusion.
The only thing I worry about on the front axle is the short back spacing and its detriment to the front wheel bearings. Of course, the Dodge has the infamous 'unit bearing' Dana 60 front end where the bearings are puny and spaced too close together for a good long life. Do you have the AAM front axle? I believe they have the upgraded bearing posture. If you have interior locking hubs, you have the better bearing set up.
jefe