Just used fleece for the first time this evening. Forcast of zero temps tonight. I've got an old small mini greenhouse (used to be polythene covered), which I've covered with fleece inside my greenhouse to save having to fleece or bubble wrap the whole greenhouse. Wrapped up the camelia outside, and hopefully everything else which matters is hardy .
ER just checked your location and you should be ok tonight, others will advise you later I'm sure.
As it turned out, I think I made the right call. The temperature went down to zero, with ice on the greenhouse glass and on the small polythene greenhouse which is right up against the wall of our house.
I keep my potted up camellias near the house during winter, which they have now survived for many years. No need for fleece. They are pretty hardy? Only problem is when they are in flower when frosts will brown the flowers.
What's in the GH, are they tender plants that you're giving some heat or borderlines that just need a little protection?
I fleeced the camelia just to give the buds a little bit of protection.
The greenhouse is wintering some half hardy lobelias, salvias, some cut back to the bone pelargoniums and just to be on the safe side a phormium.
I think it's the white flowered camellias that are more easily damaged by frost/ thaw. Camellias themselves are tough but the flowers get damaged by a quick thaw after frost. A fleece cover should be sufficient
No need to worry too much tonight here ....9 degrees.