....New to me '14 Xpress Catfish that has limited storage but does have a lod rocker that can hold about 8 rods. Inside is carpeted but today, after a plug mishap and getting water in the boat, I noticed it soaking wet. Upon inspection, the water is coming in thru the seam between the floor and side (circled in red on a stock boat photo since its to dark now to take a pic of mine). Xpress just lays down several nice, but just tacks welds that obviously doesnt seal the locker. Is there a GOOD QUALITY sealant/silicone that would last that I can run a bead along the seam and try and seal it up?

3M 5200 marine sealant you can find at Sports Academy good stuff.

5200 is VERY messy stuff, and is far more than just a sealing silicone. It is very tacky, clean-up is difficult, and it is very permanent. (I've seen it rip large areas of gelcoat off a fiberglass boat when a jackplate was removed.) The "get it everywhere goo factor" of 5200 is not easily expressible.

What you want to seal is for convenience, not critical integrity of the boat. Academy also sells a tube of 3M clear Marine silicone sealant that I have used quite a lot on my boats and I've found it to be adequately tenacious in not letting go, even on slick gelcoat. I suggest you do as much as you can to push the sealer into the seam, even using gloved fingers to force it in further. Cut the applicator tip at a small diameter so you can get the product aimed into that seam as well as you can.