Range and size/weight, of tanks are considerations, if you have a vehicle that sees limited miles driven from the fill station, then propane makes sense, because the tank size is small and the added tank weight because of the availability of re-fill . If you tried to duplicate the range of the 100 gal fuel tank, in most M/Hs, with propane system you would eliminate most of the basement space and CCC of most M/Hs.
The current propane tank on my M/H holds 28 gals , even without the efficency loss ; propane vs Gas or diesel ; I cant imagine carrying 4 or 5 of those.
I did , propane and N/G conversions for years, and even my own P/U to N/G. the range on a N/G fill was 120 miles, cost was 1/2 that of gas at the time, but the tanks were designed to handle 6,000 PSI and weighed way more than any 10 tanks of gas, and took up an area 2' X 2' X 5'.in the P/U box.
Because of the limited range all N/G conversions we did were dual fuel.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.