Second attempt. I cut out a piece of hard cardboard (almost plywood consistency) which I found from the back of a old picture frame. Made the mounts for the motors from a sheet of aluminium. I had a set of screws and risers that are used for installing motherboards inside a computer case. I traced out the holes and used the risers to make a platform for the arduino board.

Tried to use a yogurt container top, cut out two slots for the wheels. Use two tiny 5V motors with rubber pads for the wheels. The container top was not regid enough to hold all the components.