As Dave stated, the standard Sunline fridge in the 2004 models is the RM 2652.
Sometimes a slightly larger (longer) one can be installed. Sunline made most of the newer cabinet layouts to accept both sizes. To have the longer one, RM 2852 (a little over 6" longer) there is a knock out panel above the fridge that has to come out and then it fits in the hole.
Here are some manuals for the RM 2652. They work well.
Sunline Coach Owner's Club - Sunline Owner's Files - Dometic Fridge Model RM2652 Parts Diagram
And since you are looking at a new one, a fresh new manual off the Dometic site http://manuals.dometic.com/download.php?file=1936
Here is a pic of our 2004 T310SR fridge setup. The space above the fridge is where the wall panel can come out and the longer fridge go.
Your 2004 Sunline should have the same setup. A question would be, did the prior owner save the wooden doors covers to go with the camper? If not, your doors most likely would have a black panel in them verses the wood.
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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