I purchased a whip for 20m from Stephen, VK2BLQ, and took the opportunity to compare reception with the end fed wire I've been using.
To my surprise, signals were much stronger, perhaps 2 S points, on the vertical. Presumably the van makes an excellent ground plane. You can see the whip on a small magnetic base in the photo here. The base is too weak for driving while attached.
Here's some video of a tune around on 20m. Nice low noise and strong signals.
Sleeping by the river meant dealing with a few mosquitos. Happily I have a net which I hung over the bed with magnets - a system which worked well. There is a benefit to having a van made of steel rather than an aluminium caravan.