Building Fort St Elmo

Havin some time to spare this weekend, I decided to start building fort St Elmo for a Great Siege game some day. You'll note it's main structure is made from large slabs of polystyrene used in housing insulation that I scavenged from various building-sites!

The figure I am using for scale purposes is a 30mm Willie from the Colonial "Dolly Grey" range.
A general view of the fort showing counter-clockwise from the left; the cavalier; the main fort itself; the original ravelin covering the main gate and; the hastily constructed ravelin of earth and fascines.
The cavalier. I'm intending to build this as a two-tiered gun platform. In it's final state it's going to be somewhat higher than the fort as was it's real-life counterpart.
The landward side of the fort. I have not yet decided whether to just cut a gateway in the curtain behind the ravelin or to put it in the recess behind the orillon of the lower demi-bastion. The former would be easier, the latter more accurate.

The next major piece of work will be to sand down the exterior faces of the fort to give the characteristic "batter" of these kind of works. After that I will need to cut out the interior courtyard of the main fort and line it with some foamcore in which I am going to be cutting numerous arches to simulate the forts casemates.

The whole work is about a metre long (or a little longer depending on how you space out the outworks) by about 60 centimetres wide.