Pro
Extra range with losing interior space
Con
Need mod plate
Filler location ? Most are filled through the rear wheel tub
They ususally leak when off road - can be fixed not such a big deal
Setup ? you should pump the sills into the main so your gauge still works
Reduced clearance - doesn't really matter IMO
Protection - the tanks need a bit of armour.
I don't know whether it would be worth the hassle if you were paying people to do it. I guess it depends on how much you value your cargo space. I have that LPG kit and have taken it to bits and mounted a 40L thank in the cargo area - it is pretty small but still works fine, you just fill up a lot
If you cargo space is paramount then the under floor system with sill fuel tanks are the way to go. If it is not such a big deal you shoudl be able to fit a 60L LPG tank running front to back in the tailgate area over the right rear wheel.
Tom