Chris you are so right here, on occasions I had to wait for the water to filter in and weigh the car down so I could get traction, DID NOT TAKE LONG that's why no carpets
On the windows though I do not necessarily agree Chris, the positive pressure would undoubtedly help but, not wanting to bring on the doom and gloom but just being sensible. Just in case bad luck strikes and you fall though ice or whatever the electric windows are unlikely to work, if you are going to sink it makes great reading about 'sitting there waiting for the car to fill up and simply open the doors and swim to safety', in reality I am not so sure I (and many others I have spoken too)would have that steady frame of mind, so either roof open (no good with rack) or the windows open, car falls through or gets stuck easier to escape.
regards
Dave
there was a test done on this, can't find the details but it was pretty horrific. basically, most of the 'expert emergency ideas' are bollocks, they just don't work. electric windows will fail. even once the car is completely full of water, you cannot open the doors because of the pressure behind them. Even manual windows can't be opened because of the pressure.
The only solution is to smash the windows, but even then, actually getting out is extremely difficult. Consider the temperature of the water (sometimes below freezing) and it's unlikely you would make it out. If your on your own in iceland and this happens, even if you manage to get out of the vehicle, your going to die. As Ran fiennes said on the top gear polar challenge, if this happens, he would rather die in the vehicle.. If you go through the ice, your going to die.
Don't forget, if you are on your side or inverted, you'll struggle to get your belts off so have them off before you go in
If you are going to attempt any kind of deep fording or fording of fast flowing rivers you need a proper window breaking tool that's easily accessible. You need a well thought out evac plan that everyone knows and understands and you need at least one, preferably more, extra vehicles with room for you all.
have a look at this, bear in mind these guys are professional divers on a well rehearsed routine.
https://www.youtube.com/watch?v=OOvhYuurX5I&list=PLyU89l33fInSxKUiDdd7WOD8SZonJbPSb&index=2
Less than 20 seconds before the car was full.
notice the drill, front seat people first, rear seats last. everyone has to know what they are doing to avoid a big scramble and log jam. In helicopter drills, it's really horrible if your the 4th man, because you have to sit and wait for everyone in front of you to get out, which means your sitting under water waiting!
If you have ever tried to break a car window you will know how much force is needed, and if your underwater you won't manage it without a proper tool.