That's very possible indeed!
You wouldn't put an antenna right next to a 2 story metal shed would you? Above it would be fine though, in fact great.
That's why I suggested making up stand-off brackets to route this section of coax away from the metal mast or use a 9ft. section of heavy wall PVC or any other non-metallic pipe.
If you look at many Ham dipoles configured with a single support like an inverted V and especially ones fed by twin lead feed line like the G5RV antenna, you will see stand-off brackets to route the twin lead feed line away from a metal mast because with this antenna, a section of twin lead feed line is part of the radiating antenna. Like the A99, the G5RV needs a 1:1 choke balun to separate the feed line section from the radiating section.
Apparently, many people are using the A99 without stand-off brackets and choke baluns after 9ft of feed line and have been able to get their antenna to tune, but they are tuning it with compromised values in the equation. To many, as long as the SWR is low, that's all that matters.
Typical insulated stand off bracket, The further way, the better though.
This is similar to how I made my own stand off brackets when I used a G5RV antenna configured as an inverted V.
I used PVC fittings to keep the twin lead feed line straight and from flopping around in the wind. With my current antenna, I switched to a 45 ft fiberglass push-up pole so I don't have to deal with this any more.
