(Home) Fuel tank and consumption

Somewhere on this board, I read that the Townace has a fuel capacity of 60 litres and that when the red light comes on, you should have something like 10 litres left. Yesterday, I had to learn the hard way that this is not true for my Liteace 2.0 TD 1991. Here is my story:
I have the habit of driving my fuel tank quite low. This is nothing too bad if you know what you are doing. With all vehicles I have owned and driven so far, I found that they had some sort of warning mechanism, which left you enough fuel for a maximum of about 80 km (50 miles) to go before you run out completely (see P.S. for an amazing solution). This means, that you can normally wait until this warning mechanism kicks in and then find your nearest petrol station. You can go another 30 km (20 miles) without worry and are even safe for 50 km (32 miles).
Well, my Liteace seems to be an exeption to this general rule. When the red light comes on, I can fill in 38 litres. I once had to fill over 40 litres, so I was wondering what the actual size was. 45? 50?
Yesterday, I went on a day trip with 3 passengers and the AC on full blast, because it was quite hot. I knew I needed some diesel along the motorway, but unfortunately, I missed a service exit just as my red light started to flicker. I was not worried at all since I knew there was another service station just 18 miles (i.e. less than 30 km) ahead. I did not even bother to switch off the AC to preserve fuel. What are 18 miles? Nothing!
Guess what
16 miles later, all my dashboard lights came on and the engine cut off. What an embarrassment (and a bit of a danger too) to walk 2 miles along the M5 to get a can of diesel! Once I had filled this in, the red light was actually off again!!!
What have I learned from this experience:
1. The Liteace has a fuel tank of about 42.5 litres capacity.
2. The reserve is less than 5 litres.
3. Never underestimate the consumption of the AC (Should I have known?)
4. Do take the red light very seriously! (Surely, I should have known!)
Now I have a nice spare can, but I do not want to keep extra diesel _in_ the car. It would be a nifty solution if you could fit it into the spare wheel under the car, but this one is too big. Has anyone heard of such an idea before? Is this a marketing opportunity?
Holger
P.S.
Good one
My Trabant. It has no fuel pump because it is gravity fed (fuel tank above the engine!). The fuel gauge is a simple dipstick you are supposed to hold into the tank and then look how wet it gets. If you run out of fuel while driving, the engine will just cut off but you have a manual reserve switch which gives you another 5 litres. If the car is still moving while this happens, you can just turn the switch and let the car pushstart itself. Otherwise restart it as usual with your key. - (#697) Holger Laux, 30 Jul 01