An easy way of getting to Holland, to start your flights from Rotterdam or Amsterdam, is to use the Stena Line rail and sail deal overnight.
Typically the inclusive ticket costs £80 single including a train ticket from London Liverpool Street, cabin on the ship and onward train travel to anywhere in Holland.
It is very easy, and I have found it to be very stress free.
The ship is huge, new, and reliable. There are no long walks as the stations are next to the docks.