Quite an undertaking, Very much like painting the Fourth Bridge. I find that these days there are so many sources of stopping places, many are listed by most of the sources but to verify the locations keep them current and include information on costs of the services, the suitable approach to the location for larger campers takes a dedicated individual supported by as many campers who visit these places and are gracious enough to share their up to date reviews of them.
I find it is a marathon task just visiting the locations on google earth and verifying and recording the GPS co-ordinates..
As with all Google Maps you also need to be on line to get the best from your file and that can soon rack up costs when on the continent.
I hear what you say about the links but most of the publishers of site guides do include some sort of attempt to prohibit the publication of their information without their express permission. Good luck anyway with your endeavours.

Thanks for your quotations, which gives me occasion to state
that Google the My Maps are links to overnight places for motorhomes located geographically.

Each official website themselves decide their advertisements and information.

Providing information on the positions,
are some web my favorites
as briefly described in my introduction to the maps.

My references to the sites is okay
verified and recognized with Google satellite images.
-
I do not know exactly how it is in England with mobile broadband.
In Denmark, stationary and traveling with free roaming connections
is cheap and efficient,
if you self want to do the motorhome as good as stationary cable connection.

So, to be online with Google My Maps while travelling,
do not have to be a problem.
No need to detailed plan your trip.

Thanks for reply Bredomobile, trying to be positive about this but cannot see how to extract GPS Co-Ordinates from your map that I can use in the Sat Nav to locate the places. Is there a way to do this?

- not diretctly at present.
If you use the connected homesite you will find coordinates.

We are many who want the overnigt position
written below the text at Youtube videofilm.
It is very easy to use Google map when uploading
in the advanced options and copy the position for the visible text.
Quite simply - and in a consistent format
 so everyone can understand it.

Here are some more links and information related to Bredomobil Gooogle My Maps - now counts about 3400 overnights' - WohnmobilStällPlatz.
Approx 350 videofilms and 55 routes geografically registred.

https://www.google.com/maps/d/edit?mid=z0TIfZfQVlmw.kzOXKqmAVqcs

A Promobil My maps: https://www.google.com/maps/d/viewer?oe=UTF8&ie=UTF8&msa=0&mid=zHz-2a1tZVfU.krr2PkvxW9rw

A Swedish map with information about getting warter and drain.
https://docs.google.com/document/d/1HX2mtYZfwze2plqg5EAKPBJ9_JNFGlO6gGOsdOv5tsQ/edit
Maps. https://www.google.com/maps/d/u/0/embed?mid=zjPF-4vWzBaQ.k7N1ai3IOVxI

You can download them all for use in your own maps.
Some only partially, individually or with limitations.

Once you have them on your own maps
you can navigate using both Google Maps (online) or Here Maps offline - free.

Do you have problems ?
- ask about the subject.

If you pass the maps to others,
you can easily get problems with constant updates on the original My Maps pages.
Communicate better and would like
links to the My maps - thank you.

It's desired to use much more positions with video films
and video films will come.
It becomes a question of whether you want to be in a joint European project for motorhomes
or be forgotten over time.
A non comercial project made of motorhome users for motorhome use on travel.

Easy to set up with no technical knowledge thanks to Google's My Maps.

A motorhomes should not spend unnecessary time choosing
between more than 5 minimal databases while traveling.

Only one map with all links is necessary
- said from 20 years of experience and the experience of being online in Europe.

A map for GPS with all the links located geographically - is what you need.

Consciously I fail many and only public videos because of very poor quality.
Lack of proper GPS position,
places that are not available update in any serious and large databases
  etc.
I'm sorry for all these well-intentioned videos as deselected by other motorhome users.
They could have been beneficial for many years in the future,
but forgotten when they do not exist on a map for GPS.
as most European motorhome in the future will travel by.