I remember this ABS repair from another well known hard sided popup only back then it was on the sunny side of the camper. Same principals though. Look at this link
http://www.apachepopups.net/SMF/index.php?topic=6645.0 and fourth post down. These guys have been making repair patches using MEK and scrap ABS for years. The latest incarnation looks like you can stop at Lowe's for the MEK and secure some ABS from kids' Legos. Hope this helps