I do believe a day at room temperature won't hurt him a bit. If you're able to provide some supplemental heat, be sure you can measure it, as Jotay suggests. You might also consider putting him in a pillow-case and then put the pillow-case in the rubbermaid you plan on using. That will serve as a bit of insulation against chilling too quickly...and will also give him a place to hide when you're not showing him.