I also did that the first time with our old Roo. I've learned since then to remove the plate at the end of the year before covering...don't have to worry about snagging it in the spring when taking the cover off. But my fix was to snip off the remaining plastic pieces flush with the brake light and then install a metal plate holder with screws into the body. I used gorilla glue and then sealant around the head. Much more sturdy than the plastic ears!
Pull-Rite 16K Super 5th
2014 Rockwood Signature Ultra-Lite 8289WS
2011 Chevy 2500HD - DuraMax (Just over 5000 miles now!)
Nights camped in 2014 - 21