There's no online VIN decoder available for Sunline VINs.
On late 1980 and newer Sunlines with 17 digit VINS, the 10th digit from the left is the year:
Sometimes I've seen people buy trailers and sellers tell them the trailer is much newer than it really is. So it's possible the trailer is a few years older if it doesn't have a 17 digit VIN. 70s Sunlines had 5-7 digit serial numbers, which preceded VINs.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9473.8 (as of 6/18/21)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR