I know you guys have been doing this a long time, but I'm wondering if you've considered the pros/cons and cost savings of bringing your toad (aka "dinghy") vs. NOT bringing it?
Obvious cost savings would be better gas mileage for your Class C without the added weight of towing plus not having to pay for the extra shipping charges on the ferries, etc.
I've never been to SE Alaska, so I'm not sure how necessary having a car in that area would be, but I have been up and down the AlCan several times. I would say you really don't need to tow an extra vehicle along with you all those miles. Everything you need along the way will be easily accessible with your class C and I doubt you'll even need to unhitch the toad (unless you really like exploring the backroads, etc...but I think you'll see PLENTY of wilderness on the AlCan itself!)
Sure, it's nice to have a car to do side trips but is it really worth the extra cost? I also realize it's much easier to have a car in the larger cities (i.e., Vancouver, Anchorage, Fairbanks), but perhaps you might consider renting a car for a few days instead? Some good deals to be had on travelocity, priceline, etc. and you could still very well come out ahead vs. the extra gas of towing all that way.
We're taking our first "big" RV trip with our current class C this summer and have decided (at least for us) that NOT towing would be more cost effective (and less hassle.)
Just a thought
Either way, have a great trip!!