I would run a line from the dmarc to a single Eero in RV2. This will be the router. Then drop an Eero in each RV unit.

This assumes you don't mind the entire RV "farm" using the same network.

I suppose you could put the main router Eero in the work box, but I'm unclear as to whether it has the space, or if heat and moisture are a real concern for whatever is in the box. If there are no environmental issues with the box, then put the main Eero on there, and then hand out an Eero to all the other RV's.

Hopefully the signal will pass through successfully.