It is fairly easy to join AF MARS. The only difficulty is you now are a temporary member and have a training callsign and have 6 months to complete. You have to take a short test, send 2 drill messages, one has to be an EEI message in a digital mode, and spend 1 hour as NCS, then you become a full member, and you have to have digital capability when you join. and of course have equipment capable of operating on AF MARS frequencies.
In the 70s and early 80s, USAF used their MARS program as an actual backup comm system. Each active base had a MARS station on the air during the weekdays, and there were several key stations on 24/7, manned by active duty airmen in the radio operator specialty- was a good training for those who would go on to work at the HF air/ground stations. I recall the training area at Keesler AFB had a room full of Heath HW-18s running into dummy loads, they used for operator training.
The affiliate members would then take over the nets in the evenings, however affiliates could check in during the day.
I was a navaid tech, but volunteered at the station on base when I was off duty.
I sent a pm with my email address.