I've ridden route 8 on a mountain bike about ten years ago. We raced it in two days, about 140 or so miles in total. Maybe more but its been a while. The road surface back then was a hard dirt road. I have no reason to think that it is any different today. There aren't any subdivisions back there...
There was lots of wildlife and two bridge crossings (or so, I can't remember). The bridges were split log variety and if passable by forty mountain bikers racing through the nether regions then passable by an Airstream.
I just drove through Tok last week (near where route 5 begins--its actually out of the Tetlin junction) and would caution you to remember to fill your gas tanks at the "Three bears" unmanned gas station in Tok. It is thirty or forty cents cheaper PER GALLON than the other stations and for the life of me couldn't explain why every station isn't this way...
As for route 5 I don't know anything about it but my Atlas, gazetter and topographical maps make this thing look to be darn well remote. If your map says closed in winter like mine...forget it after September. You may want to find someone who has driven this one previously and within the last year. These dirt roads can change dramatically and there is the ever-present danger of wild fires.
Let me know when you plan upon doing it. I'll ask some folks that I know if anyone has done that road. Sounds cool! Good luck!
"Few things are impossible to diligence and skill" -Samuel Johnson