First off cool project, would like to see pics of the process. You need a mig welder for patches. I would go with a name brand, Its worth it in the long run. I have an old portable sandblaster that works great. for the size of your project it might be worth it to get ahold of one. IMO bondo has its purpose as long as you mix it right and use it sparingly. Actually, Blazin is the man to ask about bodywork.