Bass tender 10.2 Questions

I just bought a used 2004 bass tender 10.2

I have a couple of questions, why every time I use my boat I get allot of water under the main hull so the deck flexes?

I only have found 3 plugs, one under the front trolling motor bracket, one in the back transom on the deck and one of the live well

?????

If it has a cooler ck that plug, I had an 11.3 Basstender it was a great small boat. also ck for a crack, should not have any more plugs than that, could have a small crack somewhere.