Thanks everybody for your contributions. I will try to digest the information and try to come up with possible solutions.

I anyway decided not to bond neutral and earth on the output of the inverter, therefore I will keep my trolley as a portable solution. But I will try to make it as save as possible by introducing an ELU.

Once I am done with possible solutions, I will publish the diagrams on this forum for discussion.

One lesson that I however learned so far is to me thorough when buying online.