Hi lisntodd,
First of all, congratulations on your new Big Country. Welcome to the Heartland family. It looks like you joined the forum a while ago so you probably already know that Heartland owners are quick to reach out with help.
To answer your questions:
We have some COAX layout diagrams in the manuals section of the forum.
Here's a link to a COAX Layout for the Big Country. It doesn't show the connections for the outside bistro, so that may take some exploration on your part. In the Universal Docking Center (UDC), you'll find 4 coax connectors for satellite. Of each pair, the right-hand connector is for the pre-wiring for a rooftop satellite dish. The left-hand connector goes to either the living area or bedroom. Sometimes the bedroom connector is in the closet, sometimes over the dresser. If you ever install a rooftop dish, you would jumper the left/right connectors in each pair. When you have a tripod mounted dish, you run coax to the left-hand connectors.
That said, sometimes the cabling and labeling gets mixed up. So try the left-hand connectors, but you never know...
Directv has 2 technologies in use. Multi-switch, and Single Wire Module (SWM). The LNB in the dish and the receivers have to match. Some receivers can do both. Others only one or the other.
Multi-switch LNBs have 4 coax connections at the dish. With that technology, you would run a separate coax line from the dish to each receiver. The coach connections are in the middle of that run. There are two issues you're likely to have with multi-switch. You may not have a satellite connection in the UDC that connects to the bistro location. The bistro TV may be set up to run some other type of connection; perhaps HDMI from the living room receiver. The 2nd problem is that if you have a DVR receiver, the multi-switch setup requires 2 coax lines to that receiver, whereas you have only one coax line. There are solutions. Often the simplest one is to run a new cable yourself.
SWM LNBs have a single coax connection at the dish. It connects to a 4-way splitter that you would probably want to mount in the UDC. Then each of the outputs can be connected to a coax line going somewhere in the coach. SWM also requires a power inserter device that you might install at the living room receiver. The SWM technology requires only one coax line to the DVR, so you don't need to run an extra line in the coach. Another advantage of SWM is that it enables "Whole House" viewing from the DVR. Any of your receivers can watch things recorded on the DVR.
I don't know if you really want to take a permanently mounted dish from home. You could create problems for yourself at home and end up paying to get them fixed. You can typically find a Slimline 3 dish, with either technology LNB, for under $100 on Amazon or Ebay. You might be able to get a Directv guy to give you one.
From the perspective of contacting Directv, if you mention RV, you may run into complications. If you just want additional receivers, they'll may give them to you for a new 2-year contract commitment and charge $6/month for each, and install them in the house. When you go on a trip, you just take them with you, set up your dish, and you're good to go.
For me, they set up a 2nd account for the RV. Then they merged that account with my home account so a single programming package works with both accounts. The home receivers and RV receivers all show up on a single bill. There was no charge for the HD DVR and HD receiver in the RV. They also gave me a new Slimline-3 SWM Dish along with the 4-way switch and power inserter. I provided the tripod. I had the RV in front of the house and the installer aimed the dish it and set up the receivers. I think they called it a "move" and charged me $20. The 2nd account approach lets me subscribe to Distant Network Services which is how you get CBS, NBC, ABC, Fox, WB when out of your local area.
I hope this all makes sense.
Don't be too hard on your dealer if they don't know the answers. It would be surprising if they did know anything about satellite.