I plasti-dipped my chrome bumper cover thing back in July of 2015 and I didn't have any chipping issues until late Fall 2017. And that's putting it through Michigan winters, smashing through brush-covered trails and generally neglecting maintenance to the 'dip at all. So I think that's a pretty good lifespan for something that's not supposed to be permanent. I'd love to just replace it with the black version of that trim piece from GM but good lord, I can buy enough plasti-dip to do four coats on my entire truck for the cost of it. I also wouldn't say I did any extreme prep to the chrome plastic ahead of time. Just washed it down real good and maybe I wiped it with some alcohol before I went to sprayin'. Just remember you have to do many thin coats vs a few heavy coats...ie, build it up slowly.
Quick side note...I finally got around to taking the old plasti-dip off so I can re-apply. It did NOT come off like you see in all the YouTube videos and whatnot (at least for me). Fun fact, WD40 melts Plasti-Dip into butter if you spray it on let it sit for 5 minutes or so. The rest came off with some slight power washing persuasion. I think the reason it was so hard for me to remove in some areas is that I didn't do thick enough (or enough) coats and the thinner it is, the harder it is to peal off...maybe? Doesn't matter, it wasn't a big deal and still easy enough (and lasts long enough) to warrant not paying for the black trim piece.