I prefer a wood base. You really don't ahve to have any woodworking skills. Take a look at a craft store such as Michael's or Hobby Lobby, or even Wal-Mart. They carry precut display bases for a few bucks in many different sizes. All you have to do is stain and seal it. I don't know how strong the foam you are talking about is, it may or may not work. Another option is to find a picture frame in the size you want and cut a piece of plywood to the inner dimensions as a base as wll. That way, all you need to do is build up the groundwork and complete it. A good base is not relly that hard to make.
Gino P. Quintiliani
Field Artillery --- The KING of BATTLE!!!