Why I will be giving it a go...
I am converting my truck for the following reasons:
1. Fueling station 1 mile from home $1. 49 per gallon
2. CNG has no particulates to speak of. This will reduce the loading on the DPF and reduce regeneration cycle and wasted fuel.
3. Figuring 18,000 miles a year the system will save me about $1900/year in fuel costs. (Not proven yet, but I believe it will be more when you include lower regen costs and longer oil change intervals. )
4. My father does conversions professionally and has now done 3 Sprinter diesel vans that work well. He has done 25+ spark ignition conversions. I am getting a substantial discount on parts and labor, so it makes it much easier decision than some of you would have.
5. Makes the inability to delete less of a problem.
Cons:
1. Will lose some bed space. I plan to deal with this by using two 5 gallon tanks placed in front of each wheelwell and up against the front of the bed. Hoping I can customize a toolbox to fit over tanks to retain useability of that space and still have it look good.
2. A second stop to refill each time I need fuel.
3. Extra weight of system (not much of an issue in these beasts)
4. Must use a system that maximizes CNG flow at cruise and cuts CNG flow when loading the motor to prevent causing peak cylinder pressure problem and popping head-gasket.
5. Tanks are expensive and have an expiration date. I was lucky enough to find a good used tank and brackets for $350 that expires in 11/2015. I am looking for a second tank that I can plumb in series at a later date.
Some good info:
http://www.rasoenterprises.com/index.php/alternative-fuels/ngv
http://www.marvinscng.com/diesel-electronic-kits.html
http://www.delucafuelproducts.com/