Yes, I have the same car, an 04 LPG Outlander. Although the tank is nominally 75 litres, you will no doubt realise by now that generally speaking, you can only fill it to about 80% of the maximum. I've never got more than 62-63 litres in, and it is somewhat dependent on ambient temperature.
The factory-fit system does give you lots of warning, and starts 'slow' flashing 50 to 80 miles before you actually need to refill. Rapid flashing means you've switched to petrol and are 'empty' on LPG. A small tip here from experience - if it is rapid flashing, then manually switch to petrol (press the button and the green light goes out) before refilling with gas, otherwise you'll stall when pulling away from the pumps.
At the moment I'm getting about 24 mpg in mixed driving, which will go up to 25-26 in the summer, still 10% short of the official figures. Overinflating the tyres (see other postings) can help - I keep mine at about 35 psi. So the practical range would be 200-220 miles.
Hope this helps