And Murray was surprised the factory was not hotter, which means at most +5C rise then, not +10C, certainly not +20C.
He was unclear about how much the plant was on, except that it was certainly on until 10:30am on the day he arrived. That would be enough to get temperatures high (think about central heating).
Think about central air conditioning instead. It will keep the temperature stable. Even if the reactor produce 20 to 40 kW the room should not get hot. The air conditioner will work overtime instead. My guess is that in Florida the air conditioning will turn on even in winter.
It will be stuffy inside the reactor shipping container and in the fake customer site, but the rest of the building should be okay.
As I said, 40 kW is like having 3 or 4 kitchen ovens running full blast, baking cakes all day long, or a crowd of 400 people in a movie theater. Commercial air conditioning can usually handle that load.