Holland is something of a surprise for many, but I would proffer the following advice:-
Choose a site well away from the Rotterdam/Amsterdam area. Either go north or (preferably) somewhere east. We found a good site somewhere around Zeist east of Utrecht - can't remember exactly where but it's in the CC book. East and south Holland is generally much nicer than the main cities for touring, but do visit the capital.
Whilst many people in Holland speak English you will often find that all signing on Dutch sites is in Dutch - English is not used - so you sometimes have to make a guess as to there meaning, which is not easy!
Holland is NOT cheap.
In two weeks we didn't once find a large supermarket of the type found in the UK. A UK Lidl is a typical size - in fact Lidl is a good shop to use over there. Aldi in Holland is very much down market and is often found in the rougher areas.
If you want to visit Rotterdam/Amsterdam/Hague go by train. The services are quick and clean and not expensive, and they do time match if you have to change trains. Parking in the cities is a nightmare, especially the glass city that is The Hague.
Note that the Dutch often go to the seaside at the weekend. Zandvoort - the old motor racing circuit - is especially popular for city dwellers - the traffic queues make the M25/M42 look like a picnic!
Finally, and most importantly, your caravan breakaway cable (brake snatch cable) MUST be attached to your towbar. It is NOT acceptable in Holland to loop it over the ball as we do here. It is an on-the-spot fine - and the Police, if bored, often park up outside Europort to stop Britush drivers who know no better.