Polyester resin will work, won't work for as long, but if it's carefully maintained can work for quite a long time.

You though always want fresh resin, polester too and the stuff from the big box stores is generally anything but fresh, usually sits on a shelf somewhere for years.

Other downside to polyester resin is it's really really stinky, you don't want to even think about doing it inside your home, maybe in a garage with the door open, maybe, oh yeah and you've got very little working time, maybe 10 minutes at normal shop temperatures.

Bill H.