Expect a sun shade to drop the temp way down and you will always be let down. They block direct sun off the dash but the air inside a closed car still cooks, so 150 is normal even with a good one. Your edges just need to actually touch the glass and the gaps stop mattering much.

Have you thought about what the stacking is actually doing to your data before you blame the software for being clunky? The reason 200 frames beat your single shot isn't magic, it's that the moon is stupid bright and you can shoot at a fast shutter with low gain, so random noise averages out while the real detail stays put. Jupiter is a totally different animal because it's tiny, dim, and spinning fast enough that your whole 200 frame run could smear the cloud bands if you take too long. Light pollution barely matters for planets since they're bright, so that's not your problem, the real fight is getting enough focal length and catching good seeing. Stick to short video clips instead of single frames, maybe 60 to 90 seconds max before rotation ruins it.