I snow foam my car and rinse with a pressure washer at low pressure, and I use a trimmed length of backer rod to seal the air vent below the rear glass. Works well enough, if you're careful.
https://www.amazon.co.uk/PATIKIL-Backer-Joints-Weather-Construction/dp/B0CT8ZH7PF/ref=ast_sto_dp_puis?th=1