Since 1.0.5 the Mk1 fuselage is hollow. I used a bunch and the Mk 1 hitchhiker to make a torus. I could EVA from the hitchhiker and make my way around the torus. Basically it's an unpressurized 1.25m version of a crew cabin shell.
I wish we could get some other parts hollowed out, like the 1.25m to 2.5m adaptor.