John, it may only get to 27* for two hours and that is not going to cause problems UNLESS it has been sitting in the low 30's for some time to cool things down. For ease of mind I would turn your furnace on at that low temp of 50* so you can sleep well at night. Make sure your water system is not pressurized so if anything freezes it has room to expand. There should be a low point drain on the plumbing system somewhere that will drain water out of the pump and other basement pipes.
"Gunner" USN Retired, Airdale
2004 Monaco Signature 44' Conquest. Detroit 60