Holland and Germany in September

My wife and I are seasoned visitors to Europe in our caravan. The club magazine printed an article "Dutch Treat" (p42 Nov 2012) and we would welcome anybody who has done this part of Holland to give us their tips including sites to stay, places to visit. We will then travel to Apeldoorn to see the Het Loo Palace, any tips?

From there we propose to travel to the Harz mountains in Germany and would especially like any tips on this region including routes to follow.

We may do the trip the other way round, Germany then back through Holland, any comments on doing it this way?

Thanks