POR 15 or Rust Bullet Which to use?

[70cst]

I saw back in Jan 04 there was a small thread on Rust Bullet. I am about to take off my bed so I can make one good LWB bed from two. When I do this I want to rust proof the bottom of the bed floor (underside) and also work on the frame under the bed. I've read info on the POR 15 and know it takes several steps to get the metall ready before applying and it's a little pricey...but I haven't seen a lot of info on the Rust Bullet product. OK...I just found a thread on the Rust Encapsulator by Eastwood. This also looks like a good product to consider...So here's my questions:
1) I would like feed back on the three products...plus/minus
2) How much do I need to buy?
3) Best place to purchase this stuff.
4) Are there other products to consider?
As always you feedback is appreciated and welcomed...I humbly await your answers.