Yup, I just found the tool of choice for me at HD. It is the Stanley Surform pocket hand plane for about $9.
As I got a response from the Garden Forum, I thought I would relate the link from vsmith, it is a 10 part video on foam construction and shows lots of easily found tools for shaping and cutting.
http://www.youtube.com/watch?v=D1D4KBB_GC4
Thanks for the suggestions.
Agree with the Surform. The curved version can work wonders with your Tippi rough cuts. I also have several metal bristled brushes I use. One has a dense head of brass bristles, and the others are narrows heads with long steel (stiff) bristles. When you are done, even rubbing your hand over the surface adds a smoothing effect.
I use the following for "shaving" the foam. I use the first two on the home depot link.
http://www.homedepot.com/webapp/wcs/stores/servlet/Search?keyword=surform&langId=-1&storeId=10051&catalogId=10053
These work well then I take a 300 grit sandpaper on a block after just to be shure.
I somehow got my first query into Garden Trains, but I am going to try again.
I have bedded with 2" Dow Blue foam and I now need to carve out an underpass. I have started with a Tippi and that is OK but my hand is not steady enough to make a smooth transition. I was planning to fill/level with Hydrocal or Sculptamold before laying the track but I still need a tool to do a better job of creating the sloping underpass.
Is there a special tool/plane/file/etc. that anyone uses to create this effect? I have tried a sanding block but it just seems to tear up the edges and not really remove material easily.