Which is the best way to go?

[floridafly]

I have recently purchased a Covington planter with fertilizer box. The planter has a good bit of rust but it is better than most I looked at. I would like to kill the rust and paint it. I plan on spraying it with Ospho to convert the rust then put a fresh coat of red paint on it. My question is this, is it necessary to take the planter apart and paint each individual part and put it back together using new nuts and bolts or is it OK to just paint it as a whole?