Nice Land Cruiser! I have a few pics of my 80 in this thread:
https://community.gotennamesh.com/t/urbana-illinois-now-a-gotenna-mesh-ambassador-city/1660
Was just vacuuming (a Dyson, thank you very much!) - I do some of my best thinking when vacuuming or showering for some reason - and thinking about your lack of success in getting a signal between your base and your mobile unit. Then I had an ah-ha moment.
I was recently doing some research on solar charge controllers, as I just acquired a couple. It noted Australia’s leading role in development of these little wonders, like MPPT charge controls on a chip we now have at very reasonable cost. It was noted that some versions do the conversion DC-AC-DC in such a way as to effectively become a tiny transmitter, so this required development of shielding techniques.
I wonder if trying shutting down the very-well used charge controller of your panel and running things on battery alone while testing might be worth a try? Just throwing that out as a possibility creating interference of some kind, if this is what you’re doing range testing with. If it makes no difference, then you’ve ruled it out as an issue. If things seem better, then it’s well worth the trouble to have checked if this seems to fit the situation you’re encountering. Just a hunch and they don’t always pan out.
Of course, could also have one bum unit on your hands. Antenna connectors can often be an issue. I’d check that, since you’re able to open things up, if only because it’s usually one of the few solder joints in a device that’s still big enough to inspect with the naked eye. But it’s also the most likely one to fail due to a physical reason.
Good luck.