The Mariners have also extended 29-year-old midfielder Mark Hudson's deal by another year.
The duo join striker Charles Ademeno, 21, who signed a two-year deal on 1 July from Crawley Town.
Ademeno came through the ranks at Southend before moving to Cambridge United, Welling, Rushden, Salisbury and then Crawley Town in 2009 where he scored 11 goals.
The Mariners will have to pay a fee for the forward because he is under 24 and was offered a new deal by the Red Devils.
Source: BBC Sport
Source: BBC Sport