5200 or 4200 is permanent. You will never be able to remove the light without serious power tools, and you can kiss that plastic goodbye.

 

I have used 5200 before and was able to remove it. Sometimes with a little help from a knife but it does come off and it does not have much of a problem with UV. Much better than silicone.

 

Why not use synthetic (EPDM) rubber chalk that has no silicone? Many or the RV and Marine centers sell this. It's great for sealing the roof line of many RVs and Travel Trailers. You'll only need a small bead all around with it.

Permatex 80338

http://shop.advanceautoparts.com/wcs...8_pri_detl.jpg