Sleeping in your car is awesome. Last August my and my girl friend did a spontaneous trip across the US, we visited 45+ states. And we did the whole thing without a sigle hotel, sleeping instead inside of my Toyota Corolla. All I did was fold the seats, throw in a cheap Walmart mattress, get super heavy tint on the rear windows and signed up for planet fitness membership. It actually worked. The key thing here is that we did it in a corolla. You can park literally anywhere overnight in a corolla. We were never bothered in any way about sleeping in that car. I don’t think anybody even knew. We would park in hotel parking lots at night a lot because cars come and go at all hours, the lot is always full and there’s no pattern of any kind that we would be intruding on. So for example if we parked somewhere and the natives recognized all the cars except that weird corolla they eve never seen, we would kind of stick out. And if you are the only car parked inside a giant, empty parking lot at 3am you are kind of sticking out. Later on I tried sleeping in residential areas though, and I’ve never been bothered or asked about it once. And I’ve done it more than a hundred times probably. If you use common sense and don’t use the world as your bathroom, you will not have a problem.

We slept inside that car with the windows closed for a couple months. Never had a problem with O2 or CO2 as far as I can tell.

I now sleep in my car regularly. It’s amazing to me that it’s not a thing to sleep in your car. It expands your horizon immensely. You don’t get it until you have yourself gotten to the point where sleeping in your car is second nature. It’s a very useful skill to have. The camp fire is a really good example.

If you were able to have a vehicle that you actually dedicated to sleeping in (I’ve kept my corolla stock, besides the tint) and were able to modify then you would be able to sleep anywhere at any time of year very comfortably. If you are interested in this then def read ahead.

So we have a guy inside a car with the windows closed. Several things will happen. First, the entire car and the air inside it will become the same temperature as outside. Second, his breath will create extremely high humidity inside the car. Third, CO2 will accumulate. Fourth, O2 will go down. This has never been a problem for me but it’s true none the less.

Ok, the only other consideration is what temperature it is outside and how humid it is outside.

If it’s cold, we have the follwing to worry about. The humidity in the air inside the car will condense on the inner surfaces of the car. This is very bad because you will have moisture under your carpet and absolutely everywhere. You won’t be able to dry it and it will probably grow mold. Second, you will just be too cold.

If it’s hot, the hot air in the car will retain the humidity longer, so condensation isn’t a problem as much. But even a little hot is too hot because your body heat will bake you in that car.

Ok, those are all the problems and considerations for sleeping in your car. Here is how you handle them.

Energy recovery ventilator. Panasonic makes some great ERVs. These are ventilation fans that have a special interchanging ducting that transfers heat and moisture from the outgoing air stream to the incoming air stream or vice verse. So what that means is that you are putting energy into keeping the humidity and temperature within a certain range, this device will allow you to replace the stagnant air with fresh air but not blow out all that energy along with the air. These units are whisper quiet and use only 25 watts of power. Every car has an air outlet somewhere near the rear bumper. If you could hook up this unit to draw air and vent air outside, you would solve O2 and CO2. You would also partially solve humidity. And you would partly solve being too hot. If you are in a closed space, you need good ventilation.

Catalytic heater. I forget the name, it’s “wave 3” or something like that. These heaters use propane but are safe for indoor use because they are catalytic, meaning the produce no CO. They are also extremely efficient. Propane is cheap and it’s everywhere. This would solve being too cold.

Air conditioner/dehumidifier. If the air outside is humid, you are going to have to dehumidify. There is no way around this. Installing a portable dehumidifier would solve this. A proper, compressor based one would be required to keep pace. These use 300 watts or more. If it’s hot outside, vent the hot part of the heat pipe to the outside. This solves the heat problem completely, as the dehumidifier is now also an air conditioner with no penalty on power or anything else. This would be trivial to implement. When it’s cold outside, you blow the hot end of the heat pipe back into the cabin and you don’t lose any heat, but humidity is controlled.

Extremely recently a fuel cell was released for use in the RV market. It runs on propane. From what I can tell it’s real — some prominent RV brands are starting to incorporate it into their products. They have made many appearances at trade events for RVs. Needless to say, this will be a revolution. Adding a fuel cell like this would allow you to dehumidify/cool the inside of the car continuously all night. Charging several kWh off the alternator is just not really an option. So, add the fuel cell and a really good battery and maybe some solar and you have power for all I’ve menioned as well as charging phones and powering other electronics.

Between all of that, you would truly be able to sleep anywhere you wanted in total comfort. The only thing I would add woul be some stealthy cameras all around the car and monitors inside so that I could quickly asses the situation if I were woken at night.

Cheers