Out of interest, I just had a look at the Winnebago Outdoors website to see what was scheduled for 2019, and I didn't see a caravan to Alaska this year. In past years they have held up to 2, 50 day tours, per season.
I'm sure there are other long distance caravan companies/organizations out there that might have plans to head north to Alaska this year, so internet search may be your best bet, if you don't think you can do better yourself, and save some money. There's a lot of info about travel to Alaska in a publication called "The Milepost" if you decided to solo it.
Either way, it's worth the drive.
One other thing I recall reading about the caravans was the requirement to have some sort of CB radio on board, for inter-caravan communications.
Good luck with it.
Mike. Comments are anecdotal or personal opinions, and worth what you paid for them.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)