A problem, no doubt. It is a pity about Carlaverock - we spent a night there earlier in the year. Three vans that night - did not speak to the others, so don't know who they were or where they came from.
However, in the North of Scotland - where a lot of visitors come in the summer - there are so many places (I have more to post when I get a moment) and even if every one of them had a no overnight sign - who would be policing it? This has been discussed before. The "travellers" are about. We passed an encampment near Invergarry last week, but here at least wild motorhomers vastly outnumber tinks.
IMHO "wilding" as most of us know it will remain available here. If we respect the spaces, do not gather in any number, and move on each night (or spend no more than a couple of nights in one place). And there are, of course, private places like Brin where there are no problems (yet!).
Can we encourage other small businesses to offer overnight parking free of charge, especially in the less remote areas. Many farm shops for example have car parks - do you know one that might be interested?
In conversation with Telstar the other day we decided that there must be people with space - a car park, a field or something, but perhaps they do not know that we would like to wild there.
Should we consider an informal "France Passion" type system - to be added to your POIs, Canalsman?
It does not provide an answer to the problem, but in the long term it may help.