MEP asked me for some photos of my LPGed Panda, so here they are:
This installation is not a dream, but it was installed by the previous owner. In the description I will add what can be done better/nicer.

As you can see the tank takes most of the space in the trunk. This one is 40l, so I should be able to tank up to 36 l of LPG. (Which I'm not, but this is due to the valve fault)
Better solution is to install a smaller tank along one of the sides.

Under the bonnet, starting from the upper left (next to the brush): LPG electro valve with a copper pipe to the exchanger. The exchanger is connected the the cooling system with two T joints visible next to the gasoline filter. This solution is a bit of a problem in the winter, since there is less heat for the cabin. The LPG from the exchanger then goes into the air filter case. This also can be done differently. The pipe doesn't have to go in from the above, but can go in from under the filter, or through the winter air intake. When using LPG you do not change the source of air (summer/winter). If the air is too warm, the engine doesn't work (by warm I mean much more then 40 degrees Celsius).
This is the most basic installation there is and the only one commonly available for carborators.
The tricky bit is sometimes changing the fuel. To do that you need some road with no lights and junctions.
This installation is not a dream, but it was installed by the previous owner. In the description I will add what can be done better/nicer.

As you can see the tank takes most of the space in the trunk. This one is 40l, so I should be able to tank up to 36 l of LPG. (Which I'm not, but this is due to the valve fault)
Better solution is to install a smaller tank along one of the sides.

Under the bonnet, starting from the upper left (next to the brush): LPG electro valve with a copper pipe to the exchanger. The exchanger is connected the the cooling system with two T joints visible next to the gasoline filter. This solution is a bit of a problem in the winter, since there is less heat for the cabin. The LPG from the exchanger then goes into the air filter case. This also can be done differently. The pipe doesn't have to go in from the above, but can go in from under the filter, or through the winter air intake. When using LPG you do not change the source of air (summer/winter). If the air is too warm, the engine doesn't work (by warm I mean much more then 40 degrees Celsius).
This is the most basic installation there is and the only one commonly available for carborators.
The tricky bit is sometimes changing the fuel. To do that you need some road with no lights and junctions.