There was a guy at OvEx AZ a few years ago who simply mounted a "Sunsetter" type retractable awning right to the side of his truck box, which I believe was an ambulance. He called the MFG and they told him it was rated for 80+ MPH when it was retracted, so as long as you don't drive faster than that, you should be OK.
IIRC, he purchased it used and was considering a Fiamma type awning, but ended up with a more stable and larger awning for less $$. It's been a few years, so the details are not quite crystal clear, but hopefully that helps.
If you are using Sikaflex 252 on a painted surface to bond the mounting brackets or housing, you need to REALLY rough up the paint or grind it off and clean the bare metal. A mate of mine did not follow the directions and bonded it right to the OEM painted exterior.