I recently spent the night in my van camped in a woodland glade and decided to try out an idea i had been thinking about for shortwave broadcast reception.
The receiver was an Eddystone EC10 which I recently restored, it has a 'floating' aerial input circuit of nominally 50 ohms. I connected the 'earth' socket to the receiver casing and the 'aerial' socket to a length of wire in the conventional way.
Instead of hanging up the wire, I laid it along the ground under the van, so it had greater capacitive coupling to the ground than it did to the van. The receiver was on the wooden 'kitchen worktop' in the van, so it had greater capacitance coupling to the van than to the ground outside. This meant that, in effect, one terminal of the aerial input circuit was connected to ground and the other was connected to the van - so the van was acting as the aerial.
The results above 5 Mc/s were quite acceptable, with excellent reception from medium-to-strong stations and hardly any interference. Below 5 Mc/s, where the capacitive coupling was ineffective, the bands were almost silent.
If I had used an earthing stake and electrically joined the receiver earth to the van body, I might have had even better results.