Have gradually designed an enclosure in which to keep a GTM atop my Honda Ridgeline. There is a knockout in the bottom to allow an external power wire entry, but my intended use is with a goofy
“lipstick” external PS. The things are not pass-through charge, but are always-on. I tested a GTM paired with one as aux power and it made it just shy of a week before becoming exhausted. Just started timing relay mode…I am guessing life will be well north of a week. The batteries charge via a micro-USB port. I got five and 4 18650 3500mAH batteries to go with, so it’s trivial to keep the next battery charging in the truck and remove the top of the enclosure and swap it in weekly.
Printed out of Taulman t-glase, so waterproof. Will mount it atop the truck (with nothing inside) and test-drive it for the rainy week we have coming up, to see if a design change accomodating an o-ring is required to seal things up. t-glase prints SLOWLY, so I am hoping not.