The only close viable solution I see is to create spare capacity in cities that support convention centers. Orlando, for example, has had more than it's share of abandoned hotels and dormitories. Possibly, if those structures are "held" by the State while being put up for sale, they can be prevented from becoming completely run-down.

To make something like this work, there would have to be spare room inventory. Either using existing rooms or keeping dis-used locations "warm".

Using existing rooms and capping capacity at say, 80% of available rooms, could provide an emergency buffer. I think most hotels and motels are not usually 100% full, so the room rates do cover a good portion of the operating expenses. However, someone will have to pay for that loss of revenue if the building reaches 80% capacity, since the other 20% will not be available for rental. Supply and Demand says that when there are nearly no rooms available, the prices can climb dramatically. That kind of one-of-a-kind pricing helps keep the profits above break-even.

Another issue here is what to do with if you need more room. You can cancel conventions and use the rest of the rooms, however, you'll lose incoming revenue. Business will go elsewhere, possibly permanently.

The other issue here is the retrofitting or hardening of the structures themselves. Since most likely they'll be needed for risks local to the area, they need to be protected from regional disasters. That adds more costs.

What do about staff? I can see a few unions having issues with people being "hired" to "run" a hotel during an emergency. Who would you use? CERT?

I can expand if anyone is interested, but I've had an idea for a while for that could shift some of this burden of disaster volunteers back to the private sector, but not resulting in a huge impact.