You're building a home in the winter in N MI. If you're outside framing all day, last thing you'll want to do is fart around with a frozen camper buried in the snow, after work.
But regardless, you haven't bought a camper yet, housing is cheap in N MI. Too cheap to bother with the expense of buying and prepping and heating a camper through a northern winter.
But if you do go forward with a camper, presume you'll have full power hookup, as inefficient as electric heaters are, they will be more efficient than running the camper furnace.
Not sure where your "fear of fire" comes from, but I'd expect, as a builder, you'd know enough about simple appliances to mitigate whatever risk is in your head.