You may want to add this:

The pieces of foam can be folded under the tool when you do not use it, so the tool can rest upside up without the blades touching the tabletop. It is probably a better idea to build a safer / more handy box.

Do this if you want to cut precise straight lines

Cut a narrow slot in the side of the tool (be sure to be centered and aligned with the mouth), then insert a small piece of plastic in the mouth and put fix it with adhesive tape (if the slot is wider than the plastic, add some heavy paper or several layers of plastic in the slot, but the piece of plastic that comes outside the slot must be thin, 0.5mm is fine, do not use thick material)

I cut two tabs in the plastic sheet so I can fix it on the wood with adhesive tape.

How to make straight grooves? Easy:

1. Using a ruler and a sharp blade, cut a 3mm depth line in the foam where you want the centre of the groove to be
2. Insert the plastic sheet in the cut, and just follow the line while cutting.

To bend the foam...

Add some adhesive tape on the backside of the foam and you can safely bend it.

I learnt this trick from Ed at Experimental Airlines and used the tool to build his Photon glider.