There was a recent discussion on the usefullness of the free car rental coupons sent along with some travel awards. It was pointed out that several of the companies allow you to combine coupons for free days.

If the are combined for say one free day and you rent for three days - can this all be accomplished at time of rental? They don't require that you return and start a new rental agreement do they?

In particular, I have a weekend trip coming up in Sept to Florida. I arrive on a Friday, depart on Sunday. I have two UA coupons. Any suggestions on best use of the coupons?