Sealing Engine Mounting Bolts

On my 1993 25hp Johnson, in addition to the regular transom clamp screws with handles you see on small motors, it has two bolt holes for adding two 5/16" bolts. I looked at how outboard bolt holes are sealed with caulking and didn't feel satisfied with the sealing ability of caulking, at least for this small engine. Therefore, I sealed the holes with rubber gaskets made out of Firestone FlashGard http://www.firestonesp.com/thruWallFlashing.aspx
These seals are under the the engine mount and under the washers, so they will not see the sun, although Flashgard is fine with the sun. I feel this is a cleaner system and easy to disassemble and assemble. Here's a drawing to get a visual:

Any thoughts or objections?

Here's the final version:

A cupla dollops of 3M 5200 does the same job- whatever works for you.

I still liked to use the 3M 5200 cause you could get that in the wood area of the transom and less chance of the transom rotting.