Here comes the useless information about checking door sticker for payload. '
That info applies to paying registration taxes but not to what you can carry.
The proper way is to check your rear axle rating and weight the actual weight.
+- 90% of short camper weight goes onto rear axle, so that is how you can calculate what TC can you drop on your bed.
You will find that with SRW it ain't much for what is available on the market.
I had air bags on 3 of my trucks in the past and loved them, when I was using them for equipment hauling, but last 2017 dually carry 6000 lb camper with no modifications.
Coming to exhaust brake, I am not afraid to drive 75 mph with my camper so even on pretty steep grades I have all around, I just let the truck roll without braking. Huge frontal area will not let you gain high speed anyway.
In 15000 miles I used engine braking only few times and it was more for convenience than for necesity.
