Hi Howard Johno here from down under.I found your rot test interesting,I did a similar test with Meranti marine ply that I used for my weekender.I started the test 12 mths ago and had a similar result to you,Meranti always worries me as I dont regard it as a durable timber,same for Oregan Pine,if not protected with paint they suffer the affects of rot ,some times surprisingly rapid.This has been my experience over the last 25 years repairing boats and houses,and the culprit is always freshwater gaining accsses some how.I still think that the proven rot preventative is linseed oil cut 50 50 with kerosene then oil based paint thinned with kerosene not turps and then oil based paint.This of course does't work with using fiberglass on timber,which I think is wrong anyway,any timber that does duty outside cries out for oil,particularly in boats.This I know will be regarded as heresy by many,wait till they have a decent impact with their boat say having to come alongside a jetty in squally conditions,the fiberglass gets cracked ,even minutely,water seeps between the ply and the fibreglass,and so begins the end of a boat,and I have seen it OFTEN! The up side is that the weekender is usually built by the owner so his or her maintaince will likely prevent such an outcome,however I think that fibrglass is best used as a solid hull not as a component in a timber hull. Something else about Oregan,it's become noticable that timber that came from the Mt St Helens area ,after the event,is very prone to decay,something to do with the age or the condtion of the trees after being partly cooked by a volcano,just a point of interest on what affects timber