Wheel self leveling system?

[TeoAlfa]

I will try to make the picture first.
We have a hyraulic trailer where all the wheels are connected to the main chassis with a hydraulic cylinder. The chassis can be lifted or lowered by adjusting the hydraulic cylinder.
But what we do when the trailer have to pass over some ground irregularities? Some wheels will touch the ground and some others won't so the chassis will take extra loads.
I have seen some boat trailers where their wheels are capable to follow these irregularities keeping its wheels connected to the ground? Could anyone tell me how this can be done?
I note that there is no suspension system (like a truck). The wheel connects to the chassis only by the hydraulic cylinder.
Thanks in advance.

 

[TeoAlfa]

Hello and thanks for your replies.
Yes, the title is a bit misleading. Wheel self-leveling system is how the system it normally called that's because i used it.
To maintain the bed level is a good thing but not absolutely necessary.
Anyway the bumps are not going to be large so the inclination of the bed not important.
My application is for a large boat trailer. The yard is level without bumps but the main problem is when the trailer gets out of the water and onto the slipway. The slipway is inclined, The trailer travels on the slipway then it must follow the transition between the inclined slipway and the level yard surface. If there is not a system where all wheels can touch the ground, the wheels of the rear part of the trailer will touch the ground while the front ones will be on the air. I need all the wheels to touch the ground during this transition.