I wish to protect a wooden grave name plaque. I have an unopened tin of Furniglas PU15 bought in 1973. It says all weather highly resistant on tin. But a label below says SATIN for INTERIOR use. Would this protect a plaque open to all weathers year round, or would it be better to buy a yachting varnish ? I will be painting over an existing clear varnish of some kind (which I will lightly sand), and the black ranch painted lettering on the plaque. Thanks !