Welcome! We are also near Reading
you will find this group a helpful bunch. we no longer have a Sunline, but owned 4 of them. If they were still in business im sure we would have bought our latest trailer from them as well. As for your model number, if you go to the FILES section, then BROCHURES, then on page 4 you can download the brochure from 1977. Sounds like you have a 15SC. We all love to see pictures! Be sure to check out the various Meet & Greets. I believe there are 6 this year. The big one is at Buttonwood, which is 2 hours from here. The rest are smaller. Shenandoah River, and rocky Gap are both 200 miles, but IMO worth the drive
hope you can make it to one or more!