I have had Directv since 2002, and take a receiver from the house when I go camping. I know Dish had "pay as you go" plans, but you would have to contact both providers to see if it's still available.
At some point the networks sued the satellite providers saying that when you were out of your Viewing area, the "local" stations lost revenue. Courts agreed and if I travel too far from home I lose those channels. Directs answer was "direct way" at $7.00/mo. That got you either the East or West coast feeds. I figure you can get the locals over the air so it's not an issue with me.
Another consideration is HD viewing. The only way to view Directv in HD with a dish on your RV is the Winegard "Travler" at about $2500.00 plus installation. There are portable dishes that will allow you to receive HD on Dish network. I have HD at home, and standard def in the trailer, after all your supposed to be "roughing it". I did purchase my SD reciever, but I lease the HD reciever. Not sure what the equipment costs are with Dish network.
Call both providers and ask lots of questions. Determine how much money your willing to spend on the satellite dish, mine finds the satellites by itself but I paid for that convienence. Lots to think about
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.