What rust proofing is best for 11 yr. old Dodge Ram 2500

The main rust problem with 3rd gen dodge trucks is rust forming around the wheel wells of the box.

The outer box panel and the inner fender well come together here and hold road debris, i.e. Road salt.
Do something there, whether it's rust proofing, cutting that seam out, or whatever. You would be very hard pressed to find a 3rd gen dodge here in WI that doesn't have rust around the box wheel wells.

Some trucks have plastic fender liners so you might have to remove that to access the area.