On my trailers I liked to drill through the sides of the trailer up near the roof line. Most of the time this will go into a ceiling mounted cabinet on the inside where you can route the cable where it needs to go...
These are for radio scanners and Ham radio things... The SAT RADIO antenna you will probably need is not a whip mounted type and probably should be on the flat roof. I hate drilling anything through the roof area...
This is on my 5th wheel...
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This is on my POPUP trailer...
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Roy Ken