Just returned from the grand. I highly recommend Moenkopi Riverworks: Grand Canyon River Rentals
We have private boats but this was the only way to go IMHO
We flew into Vegas, shuttled to Lee"s, where we were met by moenkopi who had rigged our boats and stayed with us thru the ranger talk. They took our travel bags and stored them while we were on the river. Excellent equipment. Four star meals, waay tooo much and excellent advice--"don't forget the downstream ferry".
The water was cold in August so it won't be warmer in Dec.
The hikes are an important part of the experience.
The night float to Pearce was one of the highlights of the trip.
Moenkopi met us at Pearce with our Vegas clothes, lunch, and after a very short derigging we were on the shuttle back to Vegas.
The trip can be divided into two parts: before Lava and after Lava.
There was a noticeable decrease in angst once we were thru Lava.
It is a life changing experience.