The project is looking good.
The leak brings something to mind that should be talked about.
I am sure that once that tank is full of water and you are bouncing through the waves that there is going to be a good amount of stress on the welds.
I am certain that welding plastic shares some rules with welding metal in that your weld joint needs to be at least 1.5T thick. Basically the completed weld needs to have at least 1.5X the thinnest base material in thickness if you were to cross section it.
If your weld is from one side only I would groove out the weld joint 45° by 66@ of the material thickness for a butt joint and even though it looks like you have a lap joint I would still groove out the lower component. In plastic it looks like the root pass is called tacking. I would make sure this step is thorough and melts all the way through the last 33%. From there lay a good solid pass filling the gap. Use multiple passes if required, making sure the base material and rod are at or near melting temp.
Once that is complete, consider doing it again with a double, like you did on the outside of the tank.
The whole project is really well executed. Just have a little bit more work to do. The benefits will pay back 10 fold when done.
Rob
