We should differentiate between shaking and rocking.
Shaking (to me) is a higher frequently, say ~2 to 5 cycles per seconds. This is probably more due to the machinery of the ship (drive shaft, propellers), which tend to transmit back through the hull some of the huge amount of force they are using. This tends to show up more aft, and in areas that are less structurally sound (like a balcony in the dining room or theater). Cabins tend not to get hit so bad, since they are metal on 6 sides, but even a small vibration can cause some loose bit of the cabin to make noise all night. (Bring duct tape, which usually can be used to secure the problem).
Rocking is the slower cycle (~5 to 10 seconds per cycle) where the entire ship moves left-right-left, or front-back-front. Due to those pesky laws of physics, the ship will move around it's center of gravity. Front to back, and left to right, this is going to be somewhere very close to the center of ths ship. Top to bottom this needs to be somewhere under the water, else the ship would flip over (I think). Since there are no passenger decks below water, the best you can do is go lower and center.
However, both the cruises you were talking about were in the gulf which tends to stay quite calm unless you happen to run into a hurricane. Well, the captain will avoid the hurricane, but it still makes waves. Anyway, rocking is nothing to worry about on the vast majority of these cruises.
Also, I think Elation has Azipods which should alleviate much of the shaking. However, if you happen to get stuck in a cabin which shakesa bit, it is just life. =shrug