Cullen headed home David Martin’s far post cross to maintain Luton’s 100 per cent record under boss Hakan Hayrettin.
Luton dominated the second half after coming under heavy pressure at the end of the first and could have won by an even great margin as the Gills keeper pulled off a string of fine saves.
He said: “It’s another win and winning is a good habit to have.
“I say it after every one of these matches, but these games carry huge significance, not just to us as a football club, but to the players themselves.
Setchell feels Bedford Town deserved their opening point at Stratford
Clubs all set for big kick-off as Bedford Town, Ampthill Town and Real Bedford begin campaigns
Bedford high jumper Gracie takes silver in Belfast
Latest Bedford & District Netball League results
TK Maxx launches free gift card giveaway to celebrate summer of Great British Sport
“We want a winning mentality running right the way through this club so that when the time comes that players are needed for the first team they can come in.
“The players showed the desire and the right attitude. The work ethic is also a big thing for us and it is something we are drumming into the players on a daily basis.
“Gillingham was a big test for us, too. They have recently had a change of manager and their players were obviously out to impress.
“We’ve played well and beaten yet another Football League club. The players can take great pride in this and all of the development matches played so far this season.”
Hatters: Justham, Trialist, Trialist, Charles, Trialist (Robinson), Stevenson, Howells, Martin, Viana, Trialist (O’Donnell), Cullen.