I guess what's really required is a description of "up north". How far north are ou really going? That ultimately will drive your total heat requirement. Up here in the "frozen tundra" called Canada, many of us carry cold-weather gear in the airplane - often the "sleeping bag" doubles as an engine cowl blanket. A preheater will do little to no good if you have nothing to hold the heat under the cowling.
As for pre-heaters, if you're going to be near electricity there is a large number of electrical heating options available. But if you're thinking about being anywhere that electricity isn't available (um, yeah, that would also mean no FBO!) then you'll need to start burning fossil fuels in order to make enough heat.
One of the slickest preheaters I've ever seen was made by the fella in the hangar next to mine. He took a sheet of plywood as a base, mounted a piece of residential ductwork to it, spaced a couple of inches above the base. In that couple of inches of vertical space he slid a high efficiency muffin fan (computer cooling fan) rated at nominal 12Vdc. Thus he had created a duct and a method of moving air through that duct. Above the fan, cut into the side of the duct are two wholes to accept the nozzles of two piezo-electrically-ignited propane torches - BernzoMatics, the kind that use 1lb propane cylinders. He installed a couple of bicycle water bottle holders to hold the propane torches in place (ain't it handy that a 1lb propane cylinder is about the same size as a water bottle!?!?!).
Preheating is accomplished by hooking a small gel cell battery to the fan, then lighting the two torches and sliding the whole heater rig into place under the engine cowling so the hot air blasts up through the cooling air exit area (keep in mind this was developed for something other than an RV - RV-specific adaptations would obviously have to be made). Warmup time is pretty short.
A word of warning though - ANY preheater which uses combustion MUST be monitored by a human 100% of the time that it's running. One doesn't want to preheat the engine by igniting the airplane or components thereof!