We are DIY for the first time LQ and wiring, I just bought a convertor,Charger and Distribution panel, I understand how the 120 side works, but on the 12 volt side I cannot figure out the wiring. On the 12 volt side in the panel I have Positive buss but there is no negative buss, how do you wire the negative side?

Two ways, you can ground everything to the frame of the trailer at the light, radio ect.. or you can bring all the grounds to the ground block inside the panel where the ground from the battery goes. I ground to the frame of the trailer, just like the mfgs. do at the point of the light or whatever.