I managed to open a cuenta corriente with the temp RUT, but only after providing work contract, rental agreement, work VISA and most importantly I had a written recommendation from a Chilean with lots of activities in the bank. If you can get somebody to write a recommendation, that should speed things up.
Alternatively, I would transfer the money with Western Union or similar service. Yes, they might charge a commision, but so will the bank (through crappy exchange rates).
When buying the car, I would let the dealer handle all the paperwork (assuming it is a reasonably trustworthy dealer). It will cost you a bit extra, but you will avoid a lot of standing in line and frustrations. I was allowed to drive away with my car the same day I paid, but the dealer claimed that it was an exception. As soon as I received my physical carnet, I had to stop by the dealer, so they could take a copy of it.


