I am not an electrician, but I helped build high voltage substations which are typically 600V and above.
I am certified RV Tech, so we had some electrical theory in class. As mentioned, some things to consider, wire size, length of run, approved panel and breakers, which have been mentioned. IF it was me, and I was close to the maximum size based on my length of run, I would go to the next larger size to be safe.
I know you have to have the ground and neutral separate in the panel and having a ground rod near the panel won't hurt.
In RV parks, they have 10-20 spots off the same transformer and the grounds run back to that ground rod for that loop of sites. It costly to have ground rods for each site, so they bond all the grounds together with 4/0 copper medium ground and tie them all together back to the ground rod in the transformer.
When laying out the ground mat for a substation, the HV code and lessons learned dictates every so many square feet a new rod is driven into the ground and that rod is then bonded to the rest of the mat. I think it was every 50 linear feet in all directions, but I never was in that part of the process.
For my application, my box, and my panel are within 20 feet of each other, but I am still going to use the correct size wire and come back to the panel for the neutral and ground and both hot wires. We converted to gas, so the DPST 30A breaker and the 50 & 70 AMP DPST breakers are not needed any longer for the furnace, so I have 150A free in the panel to provide a 50A for the motorhome. It just means getting dirty and fiberglass all over me when I run the wires.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech