Ahhh....well, I've had mine on carpet over concrete spans (apartment), concrete slabs on earth (basement), and carpet over concrete over earth (basement.) In no cases did I have an issue. In the first place, I was lucky on spills and leaks, and in the second place none were over 180 gallons.
On the carpet over wood over concrete one, which is closest to your case (not identical), I personally installed a wood subfloor in my basement before having someone carpet it. In that case, like you, I knew exactly where the tank was going, so I purposely over built the subfloor where the tank would rest so there would be no indentation once I removed the tank. I placed the tank and stand over 1/2" plywood.
It was there for 3-4 years, and then I moved. Except for the carpet showing a slight depression under the panel it was fine. I think you could similarly over build the support on the hardwood floors, use a piece of carpet for padding, and place the tank. When you move, toss away the carpet.Ultimately, with some flooring you have an element of luck regarding water spills. However, stained wood floors can be easily resurfaced (I know, I had an entire main floor of my house done to revitalize 20 year old floors and it also wasn't expensive), while warped wood floors can be something else entirely.