My buddy also runs the BFG 315 and tows at max cap. Never has had a problem with the BFG's. He has a 3500 LB SRW and has the biggest camper you can get on the back plus tows a big boat.He is actually overweight on the rear axel when fully loaded.
Running the those tires have never been an issue. The stock rim will fit but they bulge the tire in the middle. I would not run those tire with stock rims. I have my spare mounted on the stock spare rim and it will fit under the truck with the 315's. Nice to have a matching spare.

 

I'm getting them put on the stock rims this afternoon. I know BFG suggests 8.5-10 inch rims but everyone I have talked to, and obviously according to the folks here, say stock is fine. My plan is to buy the Procomp Extreme Alloys (17x9) in the spring...spread out the cost.

 

I can see why people put these tires on as soon as they drive off the lot with a new Ram...they just look right.