I thought about it, then cancelled the idea:
a) Uno is not long enough to allow using the tank that fits instead of the spare wheel - the rules setting the deformation zone cannot be met.
b) Standard cylindrical tank in the trunk would occupy far too much room and the car would become impractical for anything but basic transport of persons.
However, as my car is equipped with carburettor, the simplest and cheapest LPG conversion kit would do. Those for SPI/cat cars are about twice the price of these basic models and I am unclear about the approval procedures for catted cars where you live.
Other than this, there is nothing to stop you from doing the conversion - a member of local forum reported running a Fire engine on LPG for 100k+ km without any problems.