Steve- have made the run over the past 2 years from west Georgia. 2014 in our TC and 2015 in our Moho to visit our kids in Anchorage. We goof off along the way and take about 22 days to get there and came back without goofing off for a daughter who was having a baby in 14 days)
We had cell phone most of the way (ATT with Canadian package) all the way to Ft St John then nothing until around Tok Alaska.
This year we did it in our 31 foot Itasca Sunstar towing a 2008 Focus on a dolly. I urge a Protect a Tow set up between the mo-ho and the tow car. Also we covered our windshield and front grill with reflectix. While it got unbelievably dirty, we had no scratching or dings in the car (no flaps on the moho).
Cracked the motor home windshield 3 times this year requiring replacement when we got home. Even though there is a good bit of chip seal roadway on the Alaska highway and much flying gravel, the windshield actually was broken all three spots in Wyoming from passing trucks.In 2014 took 3 rocks to the pick up windshield and only had small dings that could be sucked out. Parked at the CG in Anchorage and 5 moho's in a row had cracked windshield
Yes to spares. We carried 3- 1 for the moho, 1 for the dolly and one for the Toad. Chances are you'll be fine but there is some very rough road in AK and the Yukon in spots and if you by chance loose a tire you best have one available because it may be hard to get one. Changing a tire?- hopefully you'd be in an area where you have and can get some roadside assistance. All that said, both years we drove up and back over 20,000 miles and NEVER saw anyone with a flat- (knock on wood)
ALWAYS drive on the top half of your tank. Fuel can be a long way away.
Suggestion -- when on dirt stretches (mostly northern Canada and AK repair zones which can be very long stretches) make sure you have your generator (assuming mounted in rear)turned off. I filled up my air filter with dust and had to search for a place to find a Cummins dealer with one.
Visa and MC cards are the predominant and about only cards recognized in Canada so have one or 2 for fuel.
The wife did a blog and if you'd like the link give me a PM
Its the trip of a life time so by all means DO IT!. You'll be fine.