You are best to just replace the entire tail light assembly for a new one. They cost about $6 - $10 at your local RV dealership parts shop.
Here's a video how to replace one. No drilling new holes, you use the existing. The video demonstrates with a pop-up, but those tail lights are pretty much all the same, identical on almost every trailer, 5er, pop-up, everything.
Click here.Edit:
I just noticed your camper is a Keystone Passport. You'll have NO problem getting a new replacement tail light fixture with the tabs. Keystone uses the same one on everything, and pretty much, so does every other brand too.