Thinking about making Future OPFOR for old miniatures

[Conquistador]

If you saw this http://www.ebay.com/itm/150995768148?ssPageName=STRK:MEDWX:IT&_trksid=p3984.m1435.l2648 then you know what my "Science Fiction Future" favorite force looks like.  Hope to post iPhone picture of Scout, Marauder, and Command figures later when I cab use the desktop to load the pictures/post to flickr.

I was thinking of an OPFOR army to oppose them that used PA type equipment for simple games.  Nothing seemed to quite fit in and I am considering building "the enemy" of my miniature soldiers.

I suspect even I can sculpt something compatible in size/style but then I would have to cast them (thinking simpler is better) and I have some questions about best options.  debating between making a mold for something like (spelling) sculpey, resin, or some other non-metal alternative.  Suggestions/guidance appreciated.

Gracias,

Glenn