Probably the hardest part will be locating the battery-but as outlined by others otherwise a simple task. Dont know what truck you have (if the charge line is already isolated from camper draining truck, though sounds like it may be). However if your planning on using 12v as refer source (as main power, you probalby do want to add a constant duty solenoid-tied directly to truck alt/battery that is controlled by trucks ign on source. Would allow running heavier wire to keep up with refer draw and generally better charging by truck when on the road. AS mentioined the 12v feed for refer controller using gas or AC is minimal- the 12v feed used for cooling on a 3way is is 17+amps and can only be used with a charge source.
At any rate sounds like you do have a handle on it-once battery location determined-ensuring truck charge source isolated from camper can run lights,refer on gas etc without truck on.
edit
Currently without a battery in camper, only time its drawing or on 12v is only if truck is on-(though you dont want to do that very long..) Could be truck only supplies 12v on the charge line when running-unknown. Once a battery is added you still dont want to run in 12v mode without a charge source-the refer will kill most batteries pretty quick. Even running, most stock setups cant really keep up. Hence if you do this Id go the added solenoid and larger charge wire to maximise charge from truck.
