I did that battle for 15 years with my Manatee. Caulk the top and leave the bottom. On the house trim (above salon windows) I did caulk both sides for about 15 feet. Water would curl around the trim and compromise the varnish from the backside. The remaining question you might have is weather to caulk and varnish or varnish then caulk. I had the best results with caulking then varnishing-make sure the caulk is flexible and paintable. I liked to raise the tape line each time I varnished to protect the caulk edge (eventually getting to about 1/8 inch above caulk line). It’s tempting to stop after 3-4 coats but power on to get several coats. UV causes cracks in the varnish and then rain does the rest of the damage. Where are you located?
