Two points for a DIY paint job. For obvious reaons they are usually completed over a long time which can lead to problems. The first is treat ANY rust either surface or pits with a good rust killer, wash and prime as per instructions. Make absolutely sure your primer is water proof as many are not, I can fully recommend Davids Zinc 182. Secondly if using filler on any area do not leave it unsealed as filler will start absorbing water straight away and many otherwise good jobs have been ruined by susequent failure due to damp filler causing rust.
PS do not be conned by the metallic fillers unless you REALLY enjoy rubbing down.
Edited by mikep12, 11 February 2015 - 10:27 PM.