The base of perisher is at 1700m.. Jindabyne is 900m ... this place is about halfway between Jindabyne and the Ski rider, just past the park entry gates.
Ski Rider is around where the regular snow cover starts, but it can vary greatly each season, especially this early on. I don't remember regular snow at the Park Entry gates (ie snow on the ground every day regardless of snow fall). It will still be cold as, but i can assure you you won't have to worry unless its a heavy dumping.
I can't commend on how much snow the roof of your equipment could safely handle, if heavy snow fell that low... just saying that its unlikely much will fall. You might get an inch during the day, or maybe more overnight. Cars parked at the ski fields (1700m) can get a 2-3 inches over night if its snowing but it doesn't snow every night.
I don't think your tarp peak will help though. The snow will just collect on the tarp at any angle, it won't fall off. Eventually it will weigh down the tarp to flat.
If the annex is prone to holding water when wet, then it might be better to pack it away if its snowing.
