The message
from Owain contains these words:

I used to have a skein of (I think ex-military) very thin but strong
twisted-twin flex with teflon insulation; 40m of something like that
would weigh next to nothing so the motorised buggy wouldn't even need to
be battery powered - the draw wire could double as power feed.

Monofilament fishing line would do fine for the first pull.

--
Skipweasel
Pay no attention to that man behind the curtain.