I don't understand why you would spend all that money on having your tank safely installed and then risk self installing that potential death trap water heater in your van???
I'll stand to be corrected but them heaters are "plug and play" so to speak, ready to go for outdoor use. There's nothing "potential death trap" about it.
Ok here is why I think it could be a death trap:
It is for outdoor use.
Does he know how to correctly test for any gas leaks?
Does he know what safety devices the heater has and how to test that they are working correctly?
Does he know how to check the flame in the heater is burning correctly?
Does he know how to check if the regulator is working correctly and that the heater is getting the correct gas pressure?
Is the gas bottle secured safely? what happens if the van rolls over in an accident and hose becomes severed/detached from bottle?
Has he provided correct ventilation for lpg in a vehicle?
does he use a c0 detector is his van ? I would imagine not as it would probably be going off all the time.
Any one of these things could kill him.