i saw a guy use blast doors to adjust for hills

3 rotor joints total.
1 front to back. Which will allow it to tilt left to right when going over uneven terrain.
1 left to right. Which will allow it to tilt up and down when going over hills.
1 top to bottom. Whick will allow it to move left and right, as im sure you already have ;p
The trick is making the joint look good for your build, but still not collide, and adjusting the rotor settings to allow proper movement and movement limitations.
Here is a basic one I made.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=585399880
Hope that helps!

for the trailer up/down problem you could just add a 2 rotor joint