Running a dash cam 24/7 and car's parked for 1-2 weeks at a time, no accessible power outlet for a battery charger
I looked into a small generator. But that's an unreasonable amount of maintenance.
Battery bank would be unruly and not healthy for the alternator
Hydrogen fuel cells are prohibitively expensive
Can't find a propane fuel cell small enough
Which leaves solar as my final option
So if something does happen you might literally have to scroll through 300+ hours worth of footage to find it? Not sure if this is at a airport parking lot, or a high traffic area, but is wiring a motion sensor to trigger the recording a possibility (not sure if that's just as much of a power drain as a camera)? Your solar panels at the most are going to get.... what 8-10 hours a day in perfect conditions if we have 12-13 hours between sunrise and sunset?
The last dash cam I looked at uses 2W at 5V (=.4A) Not sure how many you plan on using, but you can get a small 5w at 12v (also .4a) charger that will sit on your dash that's smaller than a loaf of bread for about $20. You can get a cheap 15-20W at 12v for $50-$100.
If it gets cloudy for three days even one camera that's a 28.8 amp drain on your battery. I'm thinking you might either need to find a way so they aren't running all the time (and we know you don't want to search through all of that), or you're going to have to use up most of that roof and go overboard to plan for bad weather days... I'm curious how this will go.
And I'm guessing if it snows on these within the first couple of days, they would be worthless.