I have owned two ZT 260s One standard SE one with LPG conversion
The cost of conversion is high, more than £2000
You will also lose a considerable amount of boot (trunk) space for the LPG tank
If you plan on doing about 5000 miles per year you will save about £500 per year which will mean it will take you about 5 years to recover your installation costs. That is in UK of course where LPG costs about 70p per litre, I suspect it is cheaper in Germany
In my humble opinion I wouldn't bother to do the conversion unless you plan to do a much higher yearly mileage
But as "our Graham" used to say "the choice is yours"
Good luck anyway
Rgds Dave