Hi Jim
Welcome to the forum. Firstly I would not advise installing the recorder in the loft. In the winter its a cold place and in the summer time it will get very hot. Those temperature changes are not good for electronics.
As for installing the cameras it is quite hard to say when we haven't seen the building this is why we survey properties. However, we would use copex outside rather than trunking, trunking is primarily used for internal cable containment.