Genuine question. Do Gillingham actually have any footballing rivalry ?
Growing up in London, the rivalry has always been Arsenal/Spurs, then more of the hooligan element was always Chelsea/Spurs, West Ham/Spurs, Millwall/Chelsea, Millwall/Everybody else.
One of the things about going to football in London, was that I'd often go and watch West Ham, Charlton (when they were at Selhurst park) or Millwall, when Arsenal were away up North and I couldn't afford to go. And that was true for lots of lads growing up in London, because basically you could choose between 3 or 4 different games on any given weekend if your team were playing away... (this is back in the days of pay at the turnstile)
Going to watch Chelsea or Spurs though in the home end, was always a massive no though.
Yes, It's probably one of the daftest rivalries in football, but it's Swindon Town and it all dates back decades...
https://www.football365.com/news/odd-rivalries-gillingham-swindon-danny-westwood-football-league
Even to this day, the nonsense continues as highlighted by this article in 2012...
https://www.theguardian.com/football/2012/apr/18/swindon-gillingham-police-row
and this in 2014...
https://www.kentonline.co.uk/medway/news/arrests-as-rival-football-fans-11539/
The simple trick to avoiding it all is keep away from the railway station and the approach leading to and from the ground. Which I know can be difficult but go have a few beers after the game until the little shhites have all gone home.

) be first choice for half a season, try and sign Orban and then have Orban and Veliz battle it out to eventually displace Richarlison.