[twindman]

On the AK trip, yes 39 mph is about right. Be VERY careful when you hit the stretch where the permafrost is melting. At my time, they put little flags along the road to warn you. So I slowed to about 25 mph on the first one. No problem, so the next one I only slowed to 40 mph. OOOPS! Very rough.
Another suggestion is to look on the net for organized tours. I looked at one of their routes and stops and just stopped at the same places. Sometimes it is difficult to find a park at the right point. If you are driving 250 miles, but there are no parks withing 50 miles either way, you have to adjust. I had no problem with fuel, but pretty much filled up at or near the overnites.

I took about 10 days from Vancouver to AK, 30 days around AK, and 10 days back to the states. So add in time to get to Canada and back. So probably around 60 days. I didn't stay anyplace longer than around 3 days, so adjust to your schedule. Good driving.
p.s So 6 weeks is probably not going to cut it. BUT, going to the Keys or Carolinas you are looking at 7-8000 miles also. So at 250 miles per day, that is 32 days with no stopovers at all. I don't think anything you want to do will make it in 42 days. As to cost, I am disgusted at rv park costs these days. Most parks along interstates in the Rockies (not sure about the midwest/east) cost probably 60-100 a night. KOAs are 10-20 more than others.