I have my Dad's old 24' wood extension ladder, using it to hang Christmas lights on my house. He was an electrician for 30+ years, and I'm sure that this ladder helped him make thousands of dollars along the way. But it needs help. The ladder is as solid as can be, but the finish is 98% gone. You can see on the insides of the uprights, where it was either varnished or lacquered at one point... probably when it was new. What do I do? To me, this is a great opportunity, as very little of the old finish exists. Just start varnishing it with an outdoor grade varnish? Polyurethane? Spar urethane? Should I thin the first coat to get it to really soak in?