Sealant for sealing fenders to inner fenders

I want to comment of some of the options mentioned here.

Foam tape: this stuff can trap moisture, better alternatives are readily available.

Silicon: in my opinion, the worst choice. Non paintable and and incredibly difficult to remove. Better alternatives are available, in fact, I would use nothing at all before using silicon.

If you want to go super inexpensive, you can get non silicon, urethane chalking at any hardware store or Walmart.