Rust avoidance

Technical Area Body, Interior & Styling
2

Afternoon all!
My car was undersealed at some point in its life (don’t know when exactly) and is very clean underneath, but I’m aware that this alone may not be enough to chase off the rust goolies in the long term. I am washing and waxing regularly using very specific high quality stuff from Dodo Juice (really great, highly recommended), so I think the outer bodywork is safe, but I have some questions about undercar rust:

  1. Do I need to make a point of pressure washing the inner wheel arches and the sills to get all of the grit/salt out?  Or will driving through rain soaked roads [li] be enough to dislodge it all?
  2. How do I know when to get it sealed again, considering that I dont know when it was last done?
  3. Any other top tips to avoid rust?
    Thanks!! [H]
3

 The rear arches have a lip on the inside where stuff can accumulate and there is a small section like a shelf behind the end of the sills in front of the rear wheel. These areas need a good blast and need specific cleaning as normal driving wont shift the debris from there.
 
I found that there was a sort of compost in those areas in one of my cars when I bought it. Sure enough rust poped up very soon even though I was particular about keeping these bits clean. 
It had alreayd spent too much time with the stuff sitting in these areas.
 
So from my expereince you should clean there bit out regularly and a underseal is sessential once the car is clean and dry if its of a certain age.
 
Jonathan