It could be a number of different model numbers, depending on how true your length is. If your trailer is truly 17' something long overall, it is probably the T-1700 or T-1740.
But, the model number is 150% irrelevant for ordering the vent. There are only three different brands of roof vents out there, and the difference is mainly in the hinge design. As long as you have the right hinge design for the replacement, it'll work.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
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