You can not beat POR-15 with a stick. Best polyurethane cover for metal that I have ever encountered, and I have been around nearly three quarters of a century. If you follow the instructions and apply their products (cleaner, metal prep, sealer and over coat that we call POR-15 it will last the life of the car plus a few decades.
That said there are few draw backs. First those spills and drips are also there for eternity so be very careful to protect whatever you don't want coated (including yourself, as if it gets on you, you have to wait until you can grow new skin beneath what is covering you now before it will come off.) If you do not properly clean and prep the surface there is a chance that the trapped oils or dirt could prevent the plastic from adhering to the metal.
Second is if you have something you do not want seen, do not cover it with POR-15, as you can not go back later and just sand it off to complete some poor done body work. It fries to a high gloss finish (unless you buy satin black) and as such will show any forty grit scratches or weld splatter. POR-15 is so tough that the only way I know how to remove it is with an acetylene torch, which is hard on the metal underneath it, and may set the car on fire.
Final draw back is the expense. the product isn't cheap and it is hard to save any left overs. You can put Saran Wrap plastic sheeting down onto the paint and leave a flat sheet under the can so that it seals up air tight. Even then there is enough oxygen in the can to form a thick skin on the remaining paint (but what is under that skin is still good to use).