HELP with bodywork

As I mentioned before, most spray bombs have no activator/hardener = soft and not durable. Whatever is under your paint is your foundation, it's like building your house on a poor foundation, it will be the weakest link and if it fails everything on top will as well. Send OldVart a PM, he's a pro and could probably give you a real world experience with that and could also clarify your sand paper question. As I mentioned before and others agreed, you will need a lot of cans of that crap and will have paid more than if you use the proper 2K. In the end you're better off to get the shop to do the entire job then try and save a few bucks doing it yourself with poor products, either that or wait until you are in a position to spray proper primer. Sorry to be a downer but it is what it is.