I just used the maglite head, the body was made from 'Fimo' modelling plastic. I rolled up a rough cylinder and pressed it well into the head. After baking in the oven at 130 C for 30 minutes I had a solid plastic handle complete with thread that could be unscrewed.(thanks to Dominic for the origins of this idea.)
I drilled the handle through to accomodate the cable and tapped one end for a cord gland. The handle is then coated where the two parts will meet, with a liberal coating of epoxy glue (I used araldite). This is to give extra strength to the joint and to enhance the waterproof seal as there are no 'o'rings at this point.
The original maglite reflector and lens are binned. A standard MR-16 12 V dichroic halogen lamp fits nicely in to the space along with an appropriate bulb socket. A glass disc (about 50mm dia)is required to replace the original plastic lens.
I wrapped the handle with some of the same heat shrink I used for the battery. I cut it to size and superglued before heating it. The webbing handle allows the torch to be used hands free by attaching round the wrist. I had a velcro/webbing thing from some old piece of dive gear this goes through a webbing loop secured with cable ties, although I will probably replace these with stainless jubilee clips.