Your 85 camper I'm assuming has the square top corner doors. The newer ones have curved top corners.
New doors are available, just get prepared for sticker shock. Not sure of your size, but they start in the $500 and up range and then there is freight. For sure, search around for best place to buy from and the price is in line.
Finding a door off a wrecked Sunline of your vintage, may be hard. And then it may need to be rebuilt as the older ones, the wood rotted out on them, but they are rebuildable. How bad off is yours? Pending what it wrong with it, may be able to be rebuilt if you have common wood working tools and some time. Do you have any pics of it? or what is left?
Here are some of the new door places.
Lippert (LCI) also makes doors. You may have to call them as not everything they offer is on their web store. Here is a place to start with LCI https://store.lci1.com/
I had them make me a new replacement cargo door 2 years ago, the cost was not that bad and they made it up in two weeks after I ordered it. But, I had to call them and ge to the correct division that handles the doors and the aftermarket sales.
Hope this helps
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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