Even though I don't own an Airstream (actually confess to an Avion) I did do the trip with a 27ft Wilderness tag along. Went from vancouver BC, to Dawson Creek and up the Alcan to Fairbanks and Anchorage. No problems except for not enough time for looking around and enjoying the local places.
If you go, a 29ft or a 25ft would be more than fine. Prepare your vehicles well and carry sufficient spares (I had no major events in the whole trip - except a lube oil and filter change!!!!!!!!).
Take your time and be prepared for anything and most of all, relax and enjoy the trip - that is what ot is all about, isn't it.
1987 Avion 34V travel trailer (the other cigar tube).
2002 Dodge CTD 3500 Dually, Auto, 4x4
1986 F250 T/C 6.9 Diesel, LB,S/C,4x4,Auto