In addition to the safety factor, I prefer diesel over propane for availability and storage capacity. In parts of the country, propane filling stations that can accommodate a 40' motorhome are few and far between. New Hampshire is one of those places, and I would guess that New England as a whole has fewer suitable locations than any other region of the USA. Diesel, on the other hand, is available everywhere and there is no shortage of filling locations for large vehicles. My MH has a 100 gallon diesel tank that will provide coach heat for a very long time.
Converting an older motorhome from propane to diesel is expensive enough to make you think hard about selling and buying a rig that is already equipped with diesel heating. I'm on the fence, but thinking hard about it. In the middle ground, it is possible to replace the enormous built-in propane tank with one or two portable tanks that are lighter and easier to fill. We rarely require heating beyond the capacity of our roof-mounted heat pumps, and we stay mostly at full-hookup campgrounds, so hot water is electric too.
2000 Holiday Rambler Endeavor 40PBD
Freightliner XC, CAT 3126B