Do not place their pots on a concrete or gravel floor. Sucks the heat of out them. You could put them on top of styrofoam and use pipe heating cable on either side to keep them at about 40F. Make certain to keep them watered get some winter gardening fabric and put it over them. Lack of water kills a lot of overwintering plants whether in-ground or in a back porch or greenhouse. Good luck!
**Anti freeze pipe wrap used to heat low tunnel a little warmer than freezing. (Winter grown broccoli and lettuce in low tunnel. Still alive and growing on 12/31/202.) 
https://www.homedepot.com/p/M-D-Building-Products-13-ft-Pipe-Heating-Cable-with-Thermostat-04341/204814421
https://www.homedepot.com/p/7-ft-x-15-ft-1-5-oz-Heavy-Floating-Row-Cover-Garden-Fabric-Outdoor-Frost-Protection-Blanket-for-Winter-Frost-Cold-HGRC1507015/315613311