Easily carried a 4000 pound camper on my '05 in signature. I did add Energy Suspension Bumpers for the overloads. They take about ten minutes to install and are less than $100. Their benefit is to engage the overloads sooner for stability. It is a very worthwhile addition and when the camper if off the truck has no affect on how it handles. Even though you don't want to modify your truck, get these.
Second I added Air Lift air bags. Inexpensive for what they do for leveling the truck and camper side to side and for being able to change the air and therefor the truck for differing loading situations, including hard cross winds. If you get these you will have a good handling truck/camper combo.
I use Torklift tiedowns as they are frame mounted and stout. Get a rubber mat and place it between the truck bed and camper to keep the camper from moving around. Carry 70+ pounds in the duals when camper is on. With these minor accessory items your truck should be able to handle up to gross with no issues. Rams are tough!