It'll would probably unnecessary to create a channel just for the sole purpose of CAS fire-missions. Players that play the role of JTACs, FO or Squad-Leaders (SLs) are allowed to sit in the pilot channel given that they follow the rule that "Pilots have priority over other players in this channel". Just a simple message/request of CAS fire-missions in the pilot channel shouldn't be enough to clutter the channel.
E.g:
SL: This is Alpha 1-1 requesting gun run on target/marker/location.
CAS: Solid copy Alpha 1-1, commencing gun run on target/marker/location.
If you also feel that the pilot channel is getting a bit noisy don't be afraid to remind players the rules of the channel or contact a staff member to moderate the channel. The pilot channel is dedicated for the pilots to communicate to each other. Remember though that this is a casual pub server so having fun is top priority whether it be working with your friends or new people you find on the server.
