In the auto engineering biz, we used to spend a lot of time finding and fixing body sealing leaks . We used a huge blower that input air through an aluminum plate that replaced a side window temporarily - held with trusty duct tape. You can find a lot of leaks simply by wetting your hand and moving it over suspect areas. Another trick that worked well is to use a theatrical smoke generator inside and watch for the smoke as it exits. One can also use a stethoscope that just has an open hose leading to the earpieces. The leaking air makes quite a noise when amplified. I've never seen the soap trick, but it looks like a good one. Cars typically have something called an air extractor at the rear that is a big one way flapper valve. If you don't plug it, all your air will leak out there.
This is a great way to diagnose a wind noise problem that is driving you crazy. On a fairly tight vehicle, you can block the air extractor and just use the heater blower motor to pressurize the vehicle.
Yes, I have achieved work / life balance.