Top scorer Pete Sheppard grabbed a brace to take his season's tally to 14 goals with Giorgio Mancini and Harvey Impey rounding up the scoring.
The result means that the Grove need just one more point to guarantee finishing outside the bottom three with Gillingham able to catch them with two wins but having a vastly inferior goal difference.
The penultimate week of the 23/24 campaign sees two short trips for Jamie Hillman's side; on Tuesday, they head for Bristol Telephones before then travelling to Bath on Saturday to take on Odd Down.