Cycling in the Netherlands Club Tour

Going to Harwich for a ferry (there’s choice of day time or overnight boat ) has the advantage of avoiding the busy M25 around London.

Perhaps spend a few days at the Delft site before the tour begins 

If you would like to visit Amsterdam then stay on a few days after the tour ends and drive to Gaasper Camping - leave your Motorhome on that site and take the metro into the city centre.

I hope it goes well. 

You might also like to consider the Hull/Rotterdam route, I live just north of Birmingham and tried it for the first time last year, it was a surprisingly  good option. With regards to campsites local to Amsterdam you might find these congested and expensive depending on the time you are visiting, I usually prefer a site a little more off patch with good transport links.