We have traveled with Adventure Caravans to Mexico several times and attended their Calgary Stampede rally this year. We are also signed up for a Louisiana caravan in 2014. They have always treated us well and delivered more than advertised during every tour. I am sure if
you decide to caravan then you will be satisfied with their service.
With a caravan you must be willing to go along with their schedule. After all, that is their promise to you and the others. However, Adventure Caravans will allow you to modify your trip if you do so in advance. For example, on our last Baja trip we did not wish to go all the way to Cabo again. In advance, we arranged to drop out at Loreto and met the caravan two weeks later at Santispac. Adventure adjusted our price for the days we were not with the group. Enroute you may also decide to kick back for a day and not take part in local events if you need a break from the routine or are simply not interested in that day's attractions. That, of course, may be done by notifying the wagonmaster.
Even though we are completely satisfied with Adventure Caravans I don't think we will caravan to Alaska. I think we would be too tempted to take interesting detours and maybe take the ferry back to Port Hardy.
Enjoy the planning. It is an interesting choice to make. Have a great trip!