We have an RV with three satellite input options. We have the King Dome on the front of the roof of the RV, a MotoSAT in the middle of the roof of the RV, and a pair of coax fittings in a bay on the outside of the RV that can be fed from an external, tripod mounted dish. Each of these three sources feeds two separate receivers in the RV, one for the front TV and one for the rear TV.
We feed the external dish source and the King Dome source into one SW21 at the front, and one SW21 at the rear Dish receiver location. We then feed the output of those into two more SW21's, one at each location, along with the source from the MotoSAT, to make all three sources available to each of the two Dish receivers. That's a total of four SW21's. The system works great.
I would suggest not having more than one source locked onto a satellite, however, as the different coax lengths would no doubt present two seriously incompatible data streams to the receivers. In other words, take care to have only one data source feeding into the network. I am extremely happy with the results from the SW21 Multi-Dish Switch.