There is huge difference how to handle less than 1000 lb camper and how to handle >6000lb camper.
Big camper usually have very strong rear bumper, who work well in supporting the floor, while on front -fresh water tank is pulling the floor down when on jacks.
I used to have 4x6, that I lately replaced with aluminium beam that I put under front wall of the camper. Easy to carry and adds a lot to stabilization.
I adjust the jack to spread the weight between them and additional support.
This way the camper sides keep the horizontal level without sagging this way, or the other.