If you have not committed to your antenna’s yet - I would look at RF Elements -
They make a 30 Deg Horn antenna, and that is more directional perhaps than others out there? (not sure what you are planning on using exactly)
The idea is if you are going a long distance - you want the most direct sending of your signal.
These things really kick butt, and eliminate a lot of the issues that one can see with interference etc…
Um for a C5c you prolly need:
So, this twist lock adapter and the horn antenna.
Do your research and make sure that those things work for what you have - but let us know if you go that route how much of an improvement you see!
Good luck and have fun out there!