If I'm doing just a five gallon batch I can put it in my 30qt pot and boil it in the kitchen. It happened once. The beer was fine. I use a 40 lb tank and have a 20 lb back up.
I heat most my water on the stove. I brew just out the back door on the porch. Packing hot water is not a big deal to me.
I bet I could fit three big burners like my stove top uses under my 60 qt pot if I built up a brew stand. Seems easier to me than hot water heater elements. One of them has no problem with five gallons. I pay less than 8 cents a kw/h here. It might be worth doing someday.