Where to start.....
First, you won't destroy your unit unless you deliberately go over frost heaves too fast. You're bound to hit one frost heave too fast, but that will be a memorable and learning experience and as long as you learn from it, your unit will be fine. I drove the Alcan the 1st time in 1974? and was under commercial pressure to make a fast trip...admittedly in a pickup with trailer but even back then the road didn't destroy the rig. In 20+ trips on the Alcan, I never had any damage that was in the "destroy" the rig realm. Admittedly, never drove an RV, but did drive everything else and the damage was limited to headlights and windshields except for a leaking gasket on an axle (happened a couple of times) and for a busted brake line..and since the cause of the brake issue was somewhere in Montana, I don't think either the gasket or the brake issues count as an Alcan issue.
How much time? Made the trip from Los Anchorage to Spokane a couple of times in less than 72 hours. Made the trip from Los Anchorage to Seattle (without intending to see any sights) in 20 days due to weather and fires (this was WAY back in the day). I also think Alaska is worth a 72 hour round trip to fly up from Houston
....my only suggestion would be to take as absolutely long as possible. As you say, you don't want to get to AK and just turn around. Equally, IMNSHO, there are many parts of Canada that you don't want to simply pass through without enjoying the trip. There are parts of BC and the Yukon that are (almost :) ) as scenic as Alaska.
When I was doing go-fast trips, I figured I would make 50 miles an hour for every hour between wakeup and go to sleep...including fuel stops, etc. and that was in a pickup, truck, whatever, not an RV. I think one would be pretty hard pressed to make 500 miles/day....and is that how you want to spend your trip?
If it were me and I was on vacation, I'd plan on taking 21 days from Seattle or Montana to get to Tok...probably would take less even with sightseeing, but why constrain yourself? Plan on a solid two months in AK, then 15 days back.....an honest 3 months round trip.
If/when I retire, I plan to take a least a month to drive/camp from Couer d Alene to Tok.