Tim,

I covered a dinghy with poly and glass , it lasted for 21 years of constant exposure to the southern sun & saltwater .It may have lasted longer , but was brought to an abrupt end when a trawler pinched it between itself and a dock .
Poly is not a glue and should not be used as such , but as a laminating layer is is equal to epoxy , now that epoxied boats have been around for 25 years people see that it is not the panacea we thought it was in the late 70's . Good boatbuilders and repair yards use both .
Epoxy has one fault that poly doesn't suffer , thermal breakdown when used topsides under dark colors .