The camper was originally equipped for a LP gas fridge. Unless the prior owner removed the gas line, you should find it, capped off most likely, in the outdoor lower vent compartment. Or they unhooked it under the camper off the main 1/2" gas line pipe. And the roof had a vent cap over the area to let the heat out. Hopefully the roof vent still exists as that has to be there for a gas fridge.
Some of the older fridges were all gas, and some had a 120 VAC element so you could run on gas or electric. If you add a new absorption fridge, you might have to run a 12 VDC wire set to the area to handle electronic ignition for the gas mode. I'm not sure they sell the older pilot fridges anymore. The electronic ignition is a good thing for an upgrade.
Hope this helps
I posted about your camper weights on your other post.
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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