I would take WinterHawk up on his offer. My first house had the floor joist set at 16" on center. It was a very old house and we were excited about finally owning a house.
Well, the water bed was a little heavy and did a lot of damage to the floor, foundation, and walls and...
At least you are smarter than we were, you are thinking about the weight before you bring it in the house. A little extra support from beneath would not hurt anything and would save you major $$$$ in repair bills later on.
Inside Every Bright Idea Is The 50% Probability Of A Disaster Waiting To Happen.