Which caulk for outboard bracket

[skylark]

Between the aluminum outboard bracket and the fiberglass/gelcoat hull is a 3" thick piece of wood that is used as a spacer.  There are four bolts that pass through the outboard bracket, spacer, hull and backing plate which is plywood.

I need to replace the spacer due to rot, it was fir.  I am replacing with treated exterior plywood.

Which caulk would you use to seal the bolt holes and adhere the spacer to the hull?  It should be removable in the future.

[CharlieJ]

Personally, I'd use 4200.

Ducking ;D