You said "I have the box up front" Do you mean a "Box of many buttons" (BOMB or properly called a Matrix Switch?) I am assuming you do.
Now, let me ask you some questions that make where I must not make assumptions because doing so will screw it up.
Make and model of sat receiver (DISH or Direct) Example Dish network VIP 211 Z or VIP-211K
How old is your RV, IE: brand new, pre 2008.
Depending on the answers I can get specific.
ON your "MAIN" (Front TV) do you change a setting on the TV to watch sat, Perhaps changing it from TV to either LINE (A/V) or HDMI in?
What I suspect:
The BOMB (For short) is a coax switcher. it selects between different COAX sources (And optionall one A/V source, that being DVD) and sends it via coax (DVD the box has a converter built in, technical name "Modulator") to wherever you send it (MAIN, TV-=2, TV-3 AUX, VCR(DVR).
But the VIP-211Z and in fact most modern Sat Receivers does not have COAX out, only HDMI and possibly modular (also known as PBy) and A/V
So the reason you can't send Sat to the rear is... You don't have the proper cable.
IF so, there are multiple solutions
Best: Run a HDMI cable from teh front to the back and install a HDMI splitter, the Sat receiver can easily drive two dislays
Use A/V out to the DVD in on the matrix switch (BOMB) some loss of quality and of course you need to switch back for DVD playback.
NOTE.. *I have a Dish VIP-211k (not a Z) it still outputs to coax, as well as A/V and HDMI.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times