Ash is the wood of choice for many of these type of racks. Yes ash rots however if you choose tight grain slow growth ash (old Trees)this wood is more dense than the younger trees that we are seeing coming to market. Also look at the weathered strip the soft/open grain is weathered away this gives me an idea of the grain pattern. Straight and tight, Ash when flat sawed has a lot of open grain and figure however when you look at the side of this same board the grain will be very tight and straight. back to the picture,If you look at the yellow strip down near the bottom and zoom in on it you can make out the grain pattern, tight and straight= strips cut off a flat sawn piece of Ash I could go on but I won't. Finish, well if its in the sun in Fla nothing is going to work really good. Problem is with all of the varnish and pollys the sun will eat them and when it comes time to refinish there will be places where the finish has pealed or cracked away from the wood. Stripping and refinishing sucks. another option that works well is an oil finish. This finish sinks into the wood and protects it from water however the sun dryes it out sooner than the pollys so it requires more matinance to protect it. the oil is easy to put on and no stripping is required, you just have to do it more often. If your the kind of guy that will keep up with it Oil is the better way to go, otherwise the best quality marine varnish will last the longest in the sun. Ash fact- Ash was used in most of the cars when they were made out of wood. It was used for it's strenght and bending properties, it was also cheap and there was a lot of it.
Bax