So, went camping this weekend, took the solar charger. Worked perfectly, some frozen bottles I had in the fridge are still frozen 5 days later. Rain came down in buckets past 2 days, so the cardboard insulator did not survive, but everything else was great!
Nice build. I'm now looking to do something similar. This mobile tool box system caught my eye as one of parts available is ventilated... Battery in the bottom, things that need cooling in the ventilated section, https://www.homedepot.com/p/RIDGID-22-in-Pro-Box-Black-226036/206291778. Then use the thinner top section for other stuff/protect the air cooled stuff from direct rain.