How to fluorinate polyethylene?
There is a simpler way to get fluorinated polyethylene.

Polyethylene is polymerized ethylene $\ce{CH2=CH2}$. As part of the polymerization, the double bond is no longer there. Polyethylene is essentially a very long saturated hydrocarbon:  $\ce{(-CH2-CH2 -)}_n.$ 



Another polymer already exists that replaces all the hydrogen atoms with fluorine atoms: poly(tetrafluoroethylene) (PTFE), made from tetrafluoroethylene $\ce{CF2=CF2}$. PTFE is a long saturated ferfluorocarbon: $\ce{(-CF2-CF2 -)}_n.$ 



The most well known trademarked brand of PTFE is Teflon. Get your coated with or made out of Teflon/PTFE. It will be easier, cheaper, and safer in the long run. If XeF2 will fluorinate polyethylene (which is reasonably inert), imagine what it could do to yyou.