Depending on where you are - you may be able to get a good number of channels over the air - with just your roof tv antenna... The standard antennas are directional - so pointing them toward the source helps.
If you have a satellite TV subscription at home - adding a dish for your RV may be practical (fenn had a good deal there...) - but do need the clear line of sight in the direction of the satellite.
Otherwise I haven't found a reasonable (to me) alternative. Might be some out there that others can point to.
(I can't use satellite at home - line of sight has too many trees when they came out to look this past spring.)
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