Joints between fenders and outer sill

[ps4330@okc01.rb.jccbi.gov (Peter Schauss x 2014)]

What, if anything should I used to seal the vertical joint between
my outer sill (rocker pannel) and the front and rear fenders.  
The joint that I am talking about is the line which runs vertically
where the outer sill section goes behind the bottom 3" or so of the
front and rear fenders.

thanks in advance,
Peter Schauss
ps4330@okc01.rb.jccbi.gov
pschauss@aol.com
1963 Austin-Healey 3000 Mk II
1980 MGB