At the end of the 2007–08 season, Barnes had made over 100 appearances in all competitions for Grimsby. Barnes started the 2008–09 season by being in the League Two Team of the Week, then he was in the team of the week again for his performance against Shrewsbury Town. Later in the season after getting a throat infection Mariners manager Mike Newell was forced to replace Barnes, and in turn swooped to sign on loan Preston North End keeper Wayne Henderson to replace him. Barnes was then made available for loan, and on 24 March, Newell rejected a loan move from Shrewsbury Town for him after the two clubs could not agree on a deal regarding wages. On 25 March, Barnes left Grimsby after being told he was no longer needed by the club, his understudy Gary Montgomery was also released. The Mariners saw out the 2008–09 campaign with Henderson and former Leeds United player Jonny Lund, as the club's two professional keepers. Non-League Barnes joined Conference North club Gainsborough Trinity on a non-contract terms in April 2009 after the club needed an emergency goalkeeper to cover for the injured Adam Sollitt, making his debut in the final game of the 2008–09 season, a 3–2 victory over Harrogate Town. Trinity manager Steve Charles praised Barnes as he was given Man of the Match in the game, but commented signing Barnes for the 2009–10 season was unlikely due to the players desire to play at a professional level. Despite this though, Barnes signed a permanent contract for the club on 9 June 2009 as well as the club signing Darryn Stamp on the same day. Barnes was joined at Trinity by a vast number of professionals as new chairman Peter Swann boosted the club's finances to sign a higher calibre of players. Barnes would start the 2009–10 season off as the club's number 1 keeper. The Holy Blues appointed Brian Little as manager who in turn brought in former Premiership keeper Gavin Ward as his Assistant Manager and second choice keeper. During the 2011–12 campaign a mid season injury sidelined Barnes for the remainder of the season. His understudy Andy Pettinger was also forced on to the sidelines, with the club having to bring in Dimitar Evtimov from Nottingham Forest on loan before signing youngster Michael Emery to deputise. Before the end of the season Trinity brought in a new first