moved plants outside help

hi just moved plants to unheated place although still in a box any ways to generate heat as root temp has droped quite low also how harmfull is it to go from say heat to fairly cold, what can i do , plants (white widow) are now in flower maby close to 3 weeks. any sugjestions would help. thanks

Can't really say unless I know what the actual temps are. You could add a propane heater if you got the cash. This will give you the added benefit of a co2 boost.