Well as far as undercoating goes... Use a torch (propane) works well. Heat up the undercoating and use a putty knife... it will come right off. It will leave a small amount of undercoating residue. To remove the rest of the residue use rags with thinner, reducer, or gas... works really good. The rest of the bottom is pretty rusty. You could sand blast but that would be pretty hard to do under the car. I would suggest "eastwood's" rust encapsulator. I am currently doing the same thing and it is working well.
