I'll try the plywood bonding and let you guys know how it goes. Might be valuable for people that just want to go the 'garf' method without support or bracing, the thickness would be limitless, lol
Joey, although the rubber starts brown and drys black it may revert back to a brown color once wet. The pond sealer I've used tends to do this but this product may be different. Good news about the potability, lets hope that Aussies don't require a certain level of liquid rubber in their water to pass guidelines. Way excited about your cost effecttive approach! Rural Canadian living can bring it's share of highway robbery(if the highway even goes that far) and any break you can get is nice.