Welcome to DCT
@Ezreal
I guess this is my bailiwick since I've been doing continuous recording on several different cams for about 5 years now. In short, yes it can be done very successfully with no additional equipment even in most summer heats, but it has it's drawbacks and issues. Probably the biggest cam issue is that you're over-stressing things and voiding warranties so expect a shortened cam life, and possibly some heat-related focus shift (which may be somewhast permanent in cheaper cams). You're also going to wear out the sd card more quickly. As to the car, it's battery can probably run a lower-bitrate cam for 12 hours without a huge loss of service life, but there will be an impact, perhaps as much as 20%. If you've got an expensive battery that can matter a lot. And you'll need to drive the car 20-30 minutes every day without fail to keep the battery charged. Also, if you receive damage while parked for a long time, it may take hours of video review to find the incident if it wasn't detected by the g-sensor and the file locked from that. Plus in that case you have to discover the damage yourself before the needed file gets overwritten. And many newer cars have computer-controlled power schemes which can make powering the cam problematic as well as sometimes setting a trouble code in the car computer related to the unexpected power draw. The upside is that you will always have complete video of everything the cam sees.
Not all cams do this equally well. Only a few do it really well, one of which is the old original Mobius with supercaps (small, discreet in many installations, accepts some really large cards). Another possibility is the B1W (expect slight non-permanent focus shift in the summer, can use some 128GB cards). The B1W also does low-bitrate recording, which is similar to constant recording but far easier on the cam, the SD card, and the car battery. You still get continuous coverage, only at a slightly lower video quality overall. I think this is going to be your best approach based on your stated wishes. I would also highly recommend a top-quality hardwire kit for whatever cam you go with which has an adjustable low-voltage cut-off setting. This will save your battery from indiscretions on your part such as it not getting charged enough by driving. With a 128GB card you'll get over 14 hours recording time and since it's done with factory firmware you still have your full cam warranty in effect. Mobius doesn't have low-bitrate recording per se, but you can set time-lapse recording up which comes pretty close in effect and you can select lower vid rates and quality to lessen the stress on it. IMHO low-bitrate while parked with a good g-sensor set-up is the ideal parking mode.
Note that many cams have built-in overheat shutdown protection which is probably a good idea for cam manufacturers and sellers, but that can also leave you unprotected when the cam decides to shut down on a hot summer day. Personally I think that this is an unnecessary 'feature' except on high-bitrate cams which run hotter than those using less processing power. For me anyway, I'd rather have the cam die a year early without warranty than to miss a recording as the way my luck goes I'd get damage 2 minutes after the cam quit (or just after the card overwrote the needed file with smaller cards). My B1W and Mobius both have given me 2+ years use and still work fine, and with their relatively cheap cost it's not much to just buy a new one every few years if need be. No promises but I think these will give you at least 4-5 years service or more in this kind of usage. There are a few other cams you might like which I think are OK for this kind of usage, but look at these two first, and if you don't like them we can discuss more options later.
Phil