pontoon decking

hey guys,been reading and reading trying to find out what to use on the underneath of a pontoon where the plywood joints are..looked everywhere for the plastic strips that go over the joints but not having any luck finding anything..i did see some sticktape but was really looking for plastic strips like thats on it now..a couple are broke and water seeps in...any ideas? thanks in advance

 

Caulk it with an exterior caulk?

 

I don't know how these are normally done but if I were doing it I'd be much more concerned about rainwater settling into the joints from above. Are the panels made from copper treated (green) plywood? is the top already sealed? Only seal the underneath if the top is completely sealed already.
I would only bother to seal the joints if I planned on using epoxy/fiberglass cloth or tape (at least 2 layers of 8-10 oz glass (one 4" layer and another 3" layer), both sides.
Alternately, a urethane adhesive caulk squeezed into the joints during assembly would be easier. However, it will be only partly effective trying to squeeze it into joints of an existing deck. Guessing you already have carpet glued down, I'm guessing you haven't seen what is sealing the top side?

 

yea,just put carpet on it a month ago..got all glue off deck, looked like the boards were together really good..couldnt even hardly see the seams...going down the lake it must slash water up against bottom of deck cause i can see the carpet getting alittle wet ...it had a ..well,looked like a piece of curved plastic along seams underneath deck,which one has broked off..thats where i see the water getting the carpet wet..thought it would be easy to just replace the plastic piece along the joint but havent seen anythang like it nowhere...

 

The carpet should be rubber backed. sounds like you have the wrong carpet for a boat.

 

yea,its rubber backed carpet