They can just temporarily convert hotels, which are underused at the moment with the effective collapse of most traveling, tourism and business trips. Hotels have good rooms, air conditioning, power, and are fairly controlled environments.
If you wanted to have cheap and easily deliverable ICUs you're probably better starting off with RVs since those are already designed around all the stuff you need to make a habitable space. Containers are great for transporting many at a time over a long distance because they stack and are also designed to facilitate fast and easy inter-modal handling (which is why the military uses them for certain facilities). Once a containers are within a few hundred miles of its destination they tend to move one (40+ft) or two (20-25ft pup trailers) at a time by truck which is the same method of transportation used for RVs (one behind a small truck or two on a flat bed behind a larger truck). Unless someone is assembling container ICUs in massive volume and shipping them across an ocean or rail transporting them across a continent I would be very, very surprised if the extra resources required to convert and ship containers to hospital rooms is lesser than the effort required to convert (and ship if applicable) existing hotels, RVs or any other structure already equipped for living in into hospital rooms.
I can't find the clip right now but in one of NY Gov Cuomo's briefings they had an guy from (I think from the Engineers Corps) talk about this.
https://en.wikipedia.org/wiki/Packaged_terminal_air_conditio...