It depends on the LNB you have on your DirecTV dish. If it's an SWM lnb, then you can in fact use a SWM splitter to feed the two receivers with one coax each. And you'll have just one coax going to the dish from the SWM power inserter. The splitter MUST be a DirecTV SWM splitter, and goes between the SWM power inserter and the receivers.
If it's not an SWM LNB, then you'll also need a SWM8 switch, which takes multiple coax feeds from the dish and does all the magic to send it all back up one coax to the receivers. The SWM8 switch requires a different power inserter than the one used for just the SWM dish.
AND - the total number of tuners amongst the receivers can't be more than 8 - for example, a two-tuner DVR, or maybe the new 5-tuner Genies. If you have DVRs, you will have multiple tuners in each receiver.
It's probably possible to get switches that support more than 8 tuners, but that would (IMHO) be serious overkill in an RV.
๐al
Fulltiming since Apr 2007 in 2000 Rexhall Aerbus, towing 2012 Honda CRV. 47 of the lower 48 so far.