I currently run an extension cord the 30 feet from my house to my coop. From that extension cord runs another 15' cord that has 3 outlets spaced every 5 feet. I have a 250 watt stock tank heater in one outlet and a single outdoor LED rope light plugged into a timer. The unused outlet has a waterproof cover on it.
Both cords are heavy duty, exterior use rated cords. It's plugged into a GFCI outlet that is under the house, protected from elements. Where the two cords meet is in the sheltered run away from rain. It is secured at both ends and at points along the length to keep it from moving and prevent plugs wiggling loose. There are drip loops at each end for extra precaution. I ran a dog tie-out cable from the house to the run that I attached my cord to with zip ties. The cable keeps the cord above head height and out of the way of the lawn mower and snow blower. It prevents the cord from sagging without having to put tension on the cord itself. Additionally, in the event that ice builds up on the cord or a branch falls on it, the cable bears the weight so I don't have to worry about the cord being pulled out.
I am on my 3rd year with this set up and it has served me well. I inspect it with the change of the seasons to make sure the attachment points are all secure, there is no rodent or UV damage to the cords, and that all plugs are well seated in their sockets and dust and cobweb free.
I feel I've substantially reduced the risks you typically read about with long-term extension cord use in an exterior application so I'm very comfortable with my setup.