Welcome @warwick!
Sorry for the late answer. There are quite a few threads regarding this subject. I did list the first ones that came to my attention:
- good discussion about solar: https://meshtastic.discourse.group/t/solar-charging-of-meshtastic-devices/
- more solar: https://meshtastic.discourse.group/t/cheap-outdoor-setup/
- solar: https://meshtastic.discourse.group/t/various-solar-panel-tests-with-conclusion/
- tips for gaining range: https://meshtastic.discourse.group/t/practical-range-test-results/
- bicycle tracking: https://meshtastic.discourse.group/t/bicycle-tracking/
- discussion on batteries: https://meshtastic.discourse.group/t/18650-battery-recommendations-for-t-beam/
- waterproofing the case: https://meshtastic.discourse.group/t/has-anyone-tried-waterproofing-a-t-beam/
- discussion of power banks: https://meshtastic.discourse.group/t/bad-mesh-performance-when-powered-with-usb-power-bank/
You might also be interested in the router mode for your stationary nodes: “mesthastic --set-router”. Furthermore, make sure that the hop limit (max TTL) will not be exceeded from the farthest nodes.
Please, share your findings and test results from the field, as real world feedback is valuable for this project.
I hope you luck for the event!