It absolutely can be done; in fact, I did last year.
Here's a travelogue thread with pictures and such.
Not all of the national parks in Alaska are accessible by road; indeed, I think only Denali and Wrangel-St. Elias are actually penetrated by roads connected to the main highway system, and a couple of the others are at least visible from roads. That, of course, is true whether you have an RV or a Humvee or some other vehicle.
The major paved roads are in perfectly acceptable condition and would pose no real trouble for any RV, though there are of course repair and construction breaks here and there. They are not glass-smooth freeways, but they are okay roads. Some of the dirt/gravel roads can be pretty rough, but far from impassable for at least a good many RVs if one exercises a little bit of caution and minds the weather. Some of them also lead to fascinating and beautiful areas.