Hi CR, If I were to go for a LPG system, I would go for a combi tank which holds both gas and petrol. this allows you to switch between the two. Petrol gives more power and it also allows you to go to a ordinary petrol station if you run out of gas. It cost a couple of hundred more but I believe the extra cost is worth it. It is interesting that the company should offer a doughnut tank as they are usually used to replace a spare wheel under the truck. A doughnut cannot be used on a VX. As for a cylinder tank, this usually goes in the back. I wouldn't personally want that either.