Dover to Calais - equipped with a small grid of wheel bender stands, but you can tie up where it most suits you in the area you are directed to.
Dunkerque to Dover - tie up where it most suits you in the area you are directed to.
Leaving Calais port - absolutely no problems. Head towards town at the first roundabout.
Entering Dunkerque - confusing to find the way in (first time) but little traffic and a nice terminal.
Entering Dover - follow the line. No problems, but lots of security checks and so, 3 in all as I remember.
Leaving Dover - follow the line. Very confusing in places, especially where you have to go through a "buzz to enter" pedestrian gate.
No problems with traffic inside the ports anywhere. I've never used the train, and have only used these particular ferries a couple of times when heading to the north of France or into Belgium. I always appreciate the flexibility of being able to turn up and go.
Useful car parking information - I found a b&b that charges £3.50 a day for secure parking, £3 a day if you have taken even just one night lodging with them. Plenty of space, no problem with needing to be back on a particular day.
http://www.farthingloe-bb.co.uk/