Plants in pots and how to protect from frost?

the day berfore this present big freeze up i found that my border soil was ideal for planting so i went and purchased a acer palmatum bi hoo which is in a ceramic pot about 12 inches across and the same depth also a dogwood in a larger plastic pot . i have the acer in my shed with a froststat heater in place but i have insulated the larger dogwood with polythene round the bottom of the plant pot and stood it on a wooden pallet in a sheltered position in the garden which at the moment has 1 foot of snow. have i done right or wrong???? should i leave these plants in their pots or should i plant as soon as this bad weather goes and where is the best position to plant this acer which was expensive. its about 4 feet high so how old will it be??/? i also purchased 15 roses which have their roots in compost surrounded with just a polythene wrap. i have also put thse in the shed for protection from the bitter frosts we are gettin here in north east england. any further advise would be very much appreciated.