Just drive up to the check in point hand over your number and passports. 1 mins later you will get your cabin keys and your lane number to drive onto the boat. Then you will then drive through a wee security check point where you may or may not be asked to open your boot. Thats it.You dont have to empty it.
At the other end you hand over your passport, it gets a quick scan and your on your way. Last couple of times I've seen the bobbies have breathalized a few drivers.
No borders at Holland, Germany or Belgium, you wont even know your driving in another country.
Bit more of a palava at our end on the way back. you can sit in a queue for half an hour waiting your turn but unless your unlucky you dont get searched and all that.
I dont fly any more, much prefer the ferry nowadays. A lot less hassle.