It's not the truck suspension that you have to be concerned about.
You can't put just any 9' camper on a short bed truck.
First off, the tailgate is not a weight supporting part of the bed. It's not meant to have a 3000lb camper bouncing up and down on it. The flimsy cables that hold it up snap from people sitting on them. Maybe not immediately, but eventually.
Second off, UNLESS it is a specific "short bed camper," the camper itself is designed to be supported along its first 8'. It's not meant to bounce down the road with an extra 18" hanging off in open air. Even with the tailgate under it. This can break the camper's back, cause structural damage. Maybe not immediately but eventually.
When people point out issues, others will chime in dismissing the concern because they hung their camper off the back or used the tailgate and the wheels didn't immediately fall off the truck. These issues surface OVER TIME.
Ultimately you can do whatever you d*mn well please. There is no laws against it. Try it yourself. Prove us right. Prove us wrong.
Putting 10-ply tires on half ton trucks since aught-four.