If the seam on the outside of the tub were it meets the swim platform is not glassed then it is doomed to leak. At least that's my experience from the ones that I have built. It's an easy fix but you will need to re-paint the glassed area. I would not fill the bracket with foam. You should not get water coming in from the bolt holes either if it was properly sealed. Lots of 5200 around the perimeter of the tub and then around each bolt hole and the body of the tub. Then you have to seal around the joint were the tub meets the hull as well.

strick

BA...mine leeks a little bit too. But its not a Hermco...its a home made ;) Fishing in a slosh water gets in via 3 deckplates, cable clam, rigging tube...you name it.

This year I added a switched bilge pump to it. I was sick of hand pumping it at the end of the day. The boat is moored and it dosnt leak at rest while moored.

I am going to try your fill it with water trick to test my 5200 :)

How old is your bracket? Don has updated the hatches to the Armstrong ones. The old ones that I had on my bracket (built 6+ years ago) were a joke, didn't even being to hold water out!
I would run a couple layers of matt up the inside of the tub and to the underside of the platform if that is in fact where your leak is. There is no gellcoat in there to grind off, so its a pretty easy fix, even to just investigate the leak.

just leak tested my homemade one for kicks. Its the deck plates. They suck. Will be able to pump out as needed this year. ;)