Rust encapsulator: Should I use?

I am wanting to paint the undercarriage and engine bay this winter on my 70 Mach 1. I was thinking of using the eastwood rust encapsulator and then topcoating with chassis black. There is not much rust anywhere on the car so my question is do I really need the rust encapsulator? Should I forget my plan and just use a primer and paint? Also do you need to take it down to bare metal for the rust encapsulator to stick? I want a good smooth appearing finish. What is my best bet? Thanks
 
If it was my car I would sand it all down, clean and spray a coat of SPI black epoxy. Next day I would seam seal and the following day spray another coat of SPI epoxy black and your done. You have up to 7 days to recoat before you have to sand the epoxy.
 
I tried Eastwood's rust convertor and encapsulator on the underside of our fox body stang last winter. There was rust in areas that I just couldn't sand well, and I didn't want to disassemble the back half of the car to do it. The converter made the task much easier, provided it worked. I'm going to wait a little longer before I judge their stuff - I want to see how well it holds up. So far no signs of the rust returning, but its been less than a year.

I have always used epoxy primer after removing all rust, and never had any issues. Like Rusty428cj, to me thats the best way to do it, but it takes more time to remove the rust compared to using a rust converter. And epoxy primer is a little more expensive than rust encapsulator.