For $300 on top of the price of a Ford Transit Connect, you can get the van with a CNG prep package that includes hardened engine seals and valves. Of course, those $300 don't give you the full CNG package. For that, you need to go to a conversion company to get the tanks and other items installed. One such company is Altech-Eco (warning, link plays an audio automatically), which claims to be the only one with an EPA certificate of conformity to do so.
Altech-Eco was at the AFVI Expo in Las Vegas this week promoting its CNG conversions, which can also be applied to new model Focuses (see here), Fusions, Mercury Milans and to F-150, F-250, F-350 and E-150, E-250 and E-350 series vehicles. Not all of these vehicles have a CNG prep package, but Altech-Eco trains Ford dealers how to install the kits in such a way that they don't need to damage or drill through any of the frame. Alteco-Eco also offers bi-fuel kits, in case you'd like to keep the gasoline option.