In the 90's my school had a large tech program teaching fleet mechancis how to do CNG conversions. Lots of utility companies were doing it but I assume they all had fueling stations in their yards and their trucks didn't travel more than one tank of fuel distant from the station.
Some marinas have CNG pumps because some sailboaters prefer CNG over propane because natural gas is lighter than air and wont sink into the bilge and cause an explosion like propane.
CNG tanks are quite different than LPG tanks. Most CNG tanks I have seen have an external layer of fiberglass.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13