I have 3 pots that have succulents (Jade) plants in. Last year they froze, and I cut off all the dead pieces and it came back to life and has grown. I have been useing a sheet and towel to cover the plants with when it drops down to 30 degrees. Is this a good cover for them, or should I be useing something different? The covers come off during rain and when the sun is shinning.

Tina - remember a crassula is a succulent. it will survive the winter with no water. zero water. if you cut it fine with the winter freeze then stop watering your crassula 3 months before the expected frost, or earlier.
the worst thing you can do is 'bag', 'tent' or keep in a humid athmosphere over a cold winter because mould and 'the anomolous expansion of water' will send the juicy leaves to their grave.
when the leaves are shrivelled / wrinkled you can bag, tent, etc the plant BRIEFLY over cold spells.
trust me ...i have lot thousands of stumps to damp winters ...a very dry tree will survive mild frosts.
so do not water from autumn to spring - slowly, slowly, slowly is the way to grow these.
p.s. before hibernation use a P:K feed - no nitrogen. i could go on ...theres much more info on our websites if u need more.
Happy Growing ...Cactus Jase