The Mariners thrashed Coleshill Town 4-0 yesterday in the second leg after a 2-1 win in the Midlands last week.
Yesterday, in front of a new record home crowd, they never looked back once Julio Arca gave them the lead just before half-time.
Gavin Cogdon's goal in the 62nd minute put the result beyond doubt, and late goals from Carl Finnigan and David Foley completed the rout.
The Mariners are now preparing to meet Cleethorpes Town in the final at the national stadium on Sunday, 21 May.