Hey bud, not dropped by in a while as I'm tied up with my little project. Your costume just gets better and better, loving all the little hexagons and details you've managed to put in to it, totally awesome
It looks like my timing couldnt be better either, ive just used resin and foam to make the lobe plate on my colonial marine helmet using XRbots technique.
Step 1. Have foam part ready
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130501_124659.jpg
Step 2. Paint on a couple layers of PVA glue (kids glue) over the parts to be coated in resin. Allow each layer to dry fully befor applying the next. The glue acts as a sort of primer that binds the foam to resin.
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130503_102641.jpg
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130503_102622.jpg
Step 3. Paint on the resin in thin layers, one at a time allowing each layer to almost cure (the resin should be slightly green and pliable as this helps each layer to bond bettet). Rotocasting resin is the one of choice as it has self levelling properties and Smooth-On 65D is the most popular. Mix batches of no more than 20ml as it usually starts to turn before being able to apply it all.
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130503_155137.jpg
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130503_155230.jpg
Step 4. Repeat until the desired thickness is achieved
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130507_190836.jpg
I found sandpaper didn't get me very far at all with the resin I used, but found a fresh Stanly blade a very good tool for both smoothing and shaping :thumbsup
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130515_003919.jpg
Step 5. Prime and paint
http://i1225.photobucket.com/albums/ee395/Can-obi/IMG_20130514_114833.jpg