To keep my plants alive I'll be adding an extra light bulb to each hoop house, a 5 gallon jug of hot water, a blank and tarp over the hoop house and I'll give the plants aminos and seaweed the night before. Aminos help with the uptake of calcium in the plant. When a plant has extra calcium pectate between the cell walls instead of water, injury to the plant is minimized in cold temperatures. It is not uncommon for lettuce plants treated with amino acids to survive hard frosts.
Seaweed can strengthen cell walls and as a result help protect a plant from frost as well.
The following are my two best plants that will probably be my keepers. Normally when plants are vining like this, I would give them a little blood meal to help push the vines along, but since my plants where in pots so long, I'd like to have the plants root more, so I've held off on nitrogen so the plant will concentrate more on roots than salad.