All great points in your post, but I'll disagree on this one. Given the large number of holes in an RV roof already for air conditioners, sewer vent pipes, bathroom vents/fans, TV antennas, ladder mounts, etc. etc. another small hole for a ham radio antenna and associated feedline is nothing. The technology to seal the roof is well known, and regular inspections are required anyway to maintain your roof warranty. I will say that being in the desert southwest (5 to 12 inches rain/year), I'm not as sensitive to the water intrusion issues as those who maintain an RV in wetter climates.