A friend in Southern California asked about expected low overnight temp of 30F degrees, which is low by So Cal standards.
As long as the rabbits stay dry and out of the wind, 30 degrees will not be a problem for them. Some rabbitries are in locations where they get sub zero overnight, so 30 degrees is okay, although your rabbits are probably not used to it every day.
So the precautions you took are reasonable. Be sure there is some ventilation because rabbits need fresh air or they tend to get sick.
Be sure they have unfrozen water during the day. Not hot, lukewarm or cold is okay, just not frozen.
If you have the hay to use, go ahead and give them some extra for bedding or use pieces of corrugated cardboard boxes for them to sit on. Any hay or cardboard that gets soiled should be removed in the morning.
That should cover it!
Have a good day!