roger, ide just use a spray can of clear varnish. criky if every second year you have to give it a quick rub back and spend 10 bucks on a can of spray who gives a rats
just don't go full gloss
scratches too easy!
on the upside to it there isn't a brush so you don't have brush marks and a stuffed brush by the end.!
my 2 bobs worth
ps i painted my son's block trolly/blocks with interior paint samples then did the same thing coated it with clear varnish spray. worked a absolute treat. 4 years down the track they still look as good as new (apart from the dents and kidz ware)