Advice on mounting transducer to aluminum boat hull

[rkz53]

I want to mount a transducer to the back of a War Eagle boat with a surface drive motor. The instructions are pretty clear on how and where it's to be located, but I hate drilling holes in any boat below the water line, I have seen some heavy plastic mounting blocks that are attached to the boat by epoxy that you use to drill into for the transducer screws. However it is only been demonstrated on fiberglass boats, not aluminum. Does anyone have any experience with these mounts and their serviceability?

ww.basspro.com/Stern-Saver-Transducer-Mounting-System/product/1411010627028/

Also, if we decide to drill straight into the transom, what sealant do you recommend using on the screws? I'm sure it has to be a special marine grade sealant to use below the water line and I don't want to use the wrong stuff.

TIA for all the replies.