Pieris can develop a lot of foliar damage in cold weather and there is always the issue of root damage from cold exposure when in containers, so I would move them to an area that can afford some protection. Never inside the house but an unheated attached garage would work. Or anywhere you can maintain relatively even but cool temperatures. You want temps that remain below 45F but never dip too much below freezing.

The only "attached" area that would offer any protection is the porch I mentioned. It is screened in but I put up clear plastic vinyl to keep the wind and snow out this year. Will that work? Would an small out door portable greenhouse work to keep them safe?

I would put them on the porch but inside the portable greenhouse to give them an extra layer for buffering. I'd put them against the porch wall/house since any warmth escaping from the house will add a bit of warmth on cold nights.

I would also consider putting a high-low thermometer out there so you have an idea of the temperature range and can keep it within the temperature range that GG gave you. On sunny days you may want to crack the door to the outdoors so that it doesn't overheat if the porch gets any sun. You don't want the plants breaking dormancy because the porch got too warm.