Hi,
I am not to sure that the 235 mm wide tires will fit without rubbing against each other. I think that model year required 215 mm wide tires, due to the smaller wheel offset. If you have 8 lugs, normally that is a 2,800 pound rated rim, and only has about 1" of wheel offset. The 10 lug like on my F-53 motorhome used the 3050 pound rated rim and 235 MM tires, and have about 1.75" wheel offset, to provide more space between the dual tires.
The 215 mm tire should be slightly less expensive. If you are happy with Copper tires, they seem to have a great reputation.
I run Michelin RIB tires with all steel sidewall construction, they are a much stiffer sidewall, and less prone to flexing while in the corners. But with your 4 tires in the back, your tires should not be flexing anyway.
Fred.