So after 2 years, my duct seal well is falling apart.  Although the duct seal worked ok, I'm looking to switch up to the foam block.

I understand that I need closed cell foam and noticed there are various types.  Will any closed cell foam work or do I need a specific type?  Also, any place local around the south bay where I can find some? 

Thanks in advance!

Cut off a piece of that foam roller I gave you. It is basically a giant pool noodle. It should be big enough even for the Dragonfly transducer.

If you are coming to SF or somewhere down the peninsula I have some 2 inch thick closed cell foam that you can cut a piece from.

I believe these foam blocks might be the same material as the big pool noodle Tim mentioned but I'll give these a try.

but they'll be cisco brand foam 

Or cut the bottom off a tupperware container and goop it inside the hull. Then lay down some duct seal around the base to make it extra water tight. And attach the transducer to the tupperware lid. I just added another transducer last wknd...took me like 20 minutes.

  It's like a poorman's HDI...since I already had the Elite 4 DSI and Elite 5 non-DSI. One transducer in the bow and one in the stern (to hopefully avoid frequency issues and also cover more water).

Can I ask what kind of "goop" fo you guys use?

Or cut the bottom off a tupperware container and goop it inside the hull. Then lay down some duct seal around the base to make it extra water tight. And attach the transducer to the tupperware lid. I just added another transducer last wknd...took me like 20 minutes.

that is EXACTLY what I did and it's still holding the original water from when I installed it 2 years ago.