Here's a similar project in a different format: Meshtastic Harbor Breeze Solar Node https://www.instructables.com/Meshtastic-Harbor-Breeze-Solar-Node/

If you want to build this specific DIY device (as it's quite cheap), then it's probably worth clicking around the video to find the relevant bits of assembly (as a good portion of the video is just demonstrating its range and weatherproofing). If you want to avoid Google seeing you watch it, I believe Freetube still works to circumvent that.

There are some written guides for building a similar device but...

• This guide and this other guide don't appear to mention how much they cost to build without looking at each part's product page.
• This guide does mention the price of the build, but it's quite expensive at $120 per unit.

Alternatively, there does exist this pre-built solar meshtastic node, which is $79.