I think I can get my hands on those, send me a PM if it's not listed around here.
The Daemon Maul would probably best be built with foam, it's both big, and repetitive. Assembling all those fins would kill your motivation; cutting out some foam trapezoids and gluing on a dozen detail bits is a LOT easier. The finished maul would probably be a lot lighter, too- once you add resin, fiberglass, and bondo.
I usually end up putting a spacer on when I resin pep parts. cardboard, paper, etc, just don't resin it to the surfaces you want nice and clean, the surface tension of resin will fillet it up to the spacer, and have to be sanded, etc.
If you have the skill, adding a small flange to the 3d model of a part sometimes helps a lot with rigidity. Placing it on a surface, propping objects inside while you resin the outside works nicely, and inversely you can use masking-tape strips across gaps, like the ends of forearms, across the joint of elbows, etc, wrapping around the outer surface while you resin the inside. YMMV.
Of course, for more specific advice, post pics.
WH40K Pepakura File Library 
