For years, I used a fiberglass telescoping flagpole attached to my fixed ladder. I did suffer several disappointing flagpole failures due to wind load. The flagpole manufacturer did replace the broken poles, suggesting an acknowledgement of potential failure during normal use.
When we got our current coach without an attached ladder, I first considered a suction mount system. For a variety of reasons, I decided that a better solution was to change from the fiberglass poles to an aluminum extending pole. I've been glad that I did, as the aluminum pole is significantly stronger; no failures in 8 years, including numerous trips to high wind areas with 2 3'X5' flags mounted.
I use a bolt on receiver hitch like this:
and a flagpole mount like this:
Easy to put up and take down the flagpole and much more substantial than the fiberglass pole systems.
Take care,
Stu