Very Nice Fort mate!
I visited Chatham Dockyard (Were the HMS Victory was built) today and I also visited Fort Amherst today which used sloped walls such as yourself, good thing is that we mate a man called Ben and he gave us a special tour, just me and my dad around the fort, in the tunnels and everything. Are you planning on making angled cannon ports like they had:
Or these:
I am actually going to start a Minifigure sized Fort Amherst. Which I could auction to raise money for the Fort.