Trying to animate a grouped object

Hello everyone. I'm having a problem where I created a floorplan level with use of a modular kit. The level is grouped together, there is a FirstPersonController object (StandardAsset) inside, and the whole group is sitting several units above a water simulation (water4Advance tool from StandardAssets).

The idea is that my floorplan level group is the interior of a ship. I'm trying to rock the ship up and down over the sea. However, after creating keyframes within the Animation panel and then pressing the Play button, the Game scene shows walls and floors of my level falling apart as the "ship" rocks.

Before I've tried parenting the floorplan to an empty GameObject and only animating the GameObject, but that didn't work. I'm assuming that this may be some issue with double transforms or something? I've tried opening up the attribute view in the Animation tab and only selecting the transforms of each piece of the level individually, but that also didn't help.