The Orignal CNG tanks are fitted under the rear carrier, So it literaly takes zero space. After market CNG cylinder would be installed where it could be seen, taking some space, If compromising on space is a option then u can opt for after market CNG
But then again, Factory fitted would be better.
Other then that, its not the best vehicle avalible, But its the only pickup avalible in the market, Even Shehzore isnt made anymore, And the Toyota Hilux is more then 14 lacks i suppose.
So Ravi is the best as the small sized pick can be squeezed into small (galiyan mohale) and make deliveries where Shehzores and Hilux cant even reach.