Connecting dish receiver to video distribution box

That is the correct problem. The coax is wired for coax signal distribution inside the coach and he needs HDMI connections between the receiver and TV.
However, there are several ways, including modifying the way the antenna connections run, to over come the problem. I don't think the OP wants to spend the kind of money required for HDMI over coax when some very inexpensive options have been presented.