I'd say if you're coming from Epcot or MK ... take the monrail to the Contemporary and then the boat to FW. It seemed like the Contemporary boats were shuttling more often than the MK boats. But you could also take the MK boat to FW.
If you're coming over from POP or one of the non-monorail parks, the best option may just be driving the rental car over to FW. They have a guest parking area in the front. You can then take an internal FW bus to the Campfire.