What are the ski field access roads like to drive on?
All ski field access roads are alpine roads so you must carry snow chains and know how to fit them.
Cardrona Ski Resort, Treble Cone Ski field and Roundhill ski field have gravel access roads. Coronet Peak and The Remarkables ski fields are sealed roads. All can be safely driven in your rental car as long as you have the appropriate insurance cover and follow instructions for when to fit chains, etc.
Read or listen to snow reports for current road conditions.