When we came back, the boat was basically sunk. The entire main hull was full of water.
When I first got my TI, I was worried about exactly the situation you describe above. I suggest you get two inflatable kayak flotation bags and afix them to the interior of the main hull, one at the bow, the other at the stern. If you purchase them from a kayak outfitter, they will have clip loops that accept medium-size carabiners that can themselves be clipped to various points in the boat's interior. Some people simply stuff their hull with pool noodles. I guess that'd work if several are used, but as for me, I just can't trust my life (and that of my wife) to such a thing. Besides, if the pool noodles aren't secured when/if the hull fills with water, they will work their way to either the bow or stern and you'll have what sea kayakers call "Cleopatra's Needle." In other words, your half-sunk boat will be bobbing vertically in the water. Yikes! This condition is nearly impossible to recover from without serious help.
As a side note, I too live in Houston
, between Tomball and Cypress, and I've been sailing at Lake Livingston. I sent you a private message & marked you as a friend. Let's hook up, buddy! I have lots of tips to share.