You actually have a 1979 Sunline, the 3810th built in the 1979 model year to be exact. It probably was then built in the 1980 calendar year.
That number you found is the VIN. Prior to 1981, manufacturers could number the VIN's any way they wanted, so that's why it's so short.
Here's a step-by-step process to post pictures, written by JohnB
Once you get some pics up, I can help you figure out what model you have.
On edit, I just went to add your coach into the registry and I found I have # 3822 as well, and it's a 17.5'...so I'll go out on a limb here and say yours is probably that length because they built them in batches. Now I'm really curious!
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