Boejangles

Hey Guys, so I've a 3d Model of a helmet (not my design) and I've had to split it up in mesh mixer to print. However the model is a hollow piece and whilst I've been able to print the majority of parts I'm running into some trouble. As I've not really much exp, I was wondering if someone here could help. I've already tried numerous orientations with no luck. I've attached an image of what is happening and one of the model in mesh mixer. Thanks for any help in advance. Lewis.