Thanks to those who did help out, especially at such short notice.
The flight went well and landed about 40 minutes drive from the launch site, in a rather wooded area but it managed to avoid the trees and landed in a grass field close to a public footpath. There was no accessible route from our parking spot less than 500m from the landing spot, so we had to drive away from the payload and round to the other side, where a dead-end road took us to the footpath. Some locals helped us out when we got close.
For the first time I flew a 3D-printed tracker/aerial holder, with the foam polystyrene being a non-structural shell around it. I've shared the designs in my TinkerCAD account; links in my blog post here: