Finally I am working on the siege towers, Film reference has been equally as handy as live models and replicas. However since there were none at the castles I visited I decided to base mine off the ones featured in Ridley Scott's Kingdom of Heaven. I was able to find suitable images from websites featuring props used on set as well as plenty of screen grabs during the final battle of Jerusalem.
However there were no interior shots of the tower and since I may consider using towers as efficient ways to navigate the level I wanted to feature this. On a forum featuring weapons of war through history there was this video with a brief construction of a tower which was exactly what I was after, so I shall combine this with my reference. Also had great videos on the engines I'd already gone and built! Gyah!