exterior skin butt joint sealing help

I am concerned with the possibility of the exterior skin 1/4 plywood butt joints leaking. Keep in mind that under each joint is 1 1x4 pine frame where the skin is glued either with titebond II or gorilla, and I plan to put a spruce trim over each joint and screw it down.
What is the best bet to seal this crack (its flush on the other end, just 3/16" wide at one end? I have thought about a 2 inch strip of fiberglass tape, but I am not that fond of using fiberglass. I searched the forum last night and found several people using a PL adhesive/sealer product applied with a caulk gun. I googled this product and read some boat building articles where this type product was used.
I am looking for suggestions to fill these gaps (to help keep out water) and perhaps a material to seal the trim wood over these gaps before I coat the exterior with 8 coats of minwax clear shield (UV inhibited). My main concern is on the top where water may stand on the flat portions for a small length of time, before evaporating or blowing off.
Lee
What is the best bet to seal this crack (its flush on the other end, just 3/16" wide at one end? I have thought about a 2 inch strip of fiberglass tape, but I am not that fond of using fiberglass. I searched the forum last night and found several people using a PL adhesive/sealer product applied with a caulk gun. I googled this product and read some boat building articles where this type product was used.
I am looking for suggestions to fill these gaps (to help keep out water) and perhaps a material to seal the trim wood over these gaps before I coat the exterior with 8 coats of minwax clear shield (UV inhibited). My main concern is on the top where water may stand on the flat portions for a small length of time, before evaporating or blowing off.
Lee