Railway design, construction, and gardening

I am finally at the stage of cutting down into my 2" thick Dow blue styrofoam to make a sloping underpass and want to know the favored way to smooth that byway?

I am doing the roughing in with a Tippi and that is OK but my hand is not steady enough to make a smooth transition. Is there a special tool/file/plane that anyone can recommend? I tried a sanding block but it is not much good.

When  I did my mining diorama I did the initial shaping with a tree pruning saw -

Then refined with the tippi cutter -

There is also a coping saw type attachment for the tippi. The foam is also easy to shape with a sharp knife or coping saw.

After shaping you can do more shaping with an exterior grade spackle or vinyl concrete patcher.

 -Brian

Theres a very good 9-part online tutorial on Youtube starting with part 1:

http://www.youtube.com/watch?v=D1D4KBB_GC4

I guess I made a mistake in posting this as I had wanted the MRR not Garden web, but thanks very much for the tips! I have watched the first 6 Youtube parts so far and have found the tool of choice.

It is the Surform pocket hand plane, right off the shelf at HD.

Different scales, but same technics

Glad we could help. BTW my tool-o-choice is a drywall saw