Tactics for the Swamp (Fortress).

To be honest, I've started playing games as races that are less popular than others. A lot of people play as Dungeon and Castle, let them play (it all started with Heroes 3, no one played as Barbarians, everyone praised Magic. So I started playing as Barbarians, and now I only play as them).
When I play Heroes 3 with friends, I either persuade them or play as Swamp myself (by the way, I've never lost).