You've hit on a lot of the problems.
The junction boxes (or at least some of them) appear to be the regular 3x3 galvanized type, not suitably sealed for outdoor use.
I'm not certain what that "sealing compound" is around the cable glands. I looked at it fairly closely and couldn't decide!
The bubble wrap and tape appears to have been some sort of attempt to provide extra weatherproofing during the winter, as it's on many of the units on the site.
Yes, there is an RCD (GFI) on some posts and just a 16A MCB on others. Each caravan has its own independent TT earth rod, so each most likely has its own main RCD internally. (There are some small distribution cabinets around the site which may house feeder RCD's as well, but as the doors were locked I couldn't tell.)
The hookup pictured above with twin-&-earth cable into a CEE plug is not the only one:
This one caught my eye as well, with two cables apparently going from breaker to trailer:
On closer inspection, I realized that one of the cables is fixed to the frame of the caravan for a few feet but then drops down to the junction box which is behind the pipe (and almost buried in the ground too!):
The feeder cables are steel-wire armored, but XLPE jacketed, not rubber.
Unfortunately, the sea air does rather a lot to promote corrosion, especially when the covering boot is not in place properly:
The SWA gland on the bottom of that box is also just the 2-part type, intended for internal use.
[This message has been edited by pauluk (edited 04-17-2005).]