Unky, if you look at mine, it's similar to your plan. Consider putting a post at the handle, also, I used the bolt through the handle right behind the trigger. Just a little added stability since you will be putting a fair bit of torque on the saw. I used a piece of 10"x10"x1" steel plate. Most steel supply shops have a fair number of square plates laying around and can be had pretty cheaply. For a more solid mounting, keep the three point base and drill 3-4 holes in the base at the corners. Drill matching holes on your bench and bolt it down with wing nuts. Then, you can easily remove it if you want to take it somewhere.
Don't forget the hearing protection, these things are horribly loud.
Now, if you figure out a more solid work surface, let us know. The dewalts have nice aftermarket ones, but I haven't found one for the HF.