Tactics for Rampart.

Good evening, could you please advise on the following situation: I was playing Rampart on a small map with ponies, and I took a secondary castle in the swamp in a corner. There's not much to take from it, as it's far away. I couldn't break through another path, so I went through the desert without a road to another secondary castle, and there I took some strong beasts/gnolls and a +3 Pandora's Box and a mine. I don't know what to build. Dragons are too expensive, archers are too far away, and it's more expensive to build a castle anyway. In the end, I gave up on building and started hoping for a third castle. When I crossed the desert, I took a flux (1-2-7) and started building birds. But they only appeared at 1-3-6. In a game with a reasonably good opponent, I feel like it's too late. What should I do?