I have another idea which you can put on the wishlist for future CCK versions:

1) open reservation form directly when you click a date on the booking calendar and add the date automatically to the rental start field.

2) block dates so rentals cannot be made for those dates

3) earliest rental day based on the current day (today is the 29th of October. The earliest rental date is the 30th of October or later). Reason: sometimes one has to prepare/service the vehicle after a rental ends and before it can be rented out again.

4) latest day an instance can be rented based on the current date (reason: many rental offices don't want that they get rental requests for rentals 9 month or 1 or more years in advance)

Thank you for your propose.

2) block dates so rentals cannot be made for those dates

This inn OrdaSoft Joomla CCK you may do now , If approve request from self to some data

Regards
OrdaSoft team