There are numerous pull thru sites at Congdon Creek, on an outer loop. The sites along the lake shore are back in, some larger than others. There is also a very large double site at the north end of the campground along the lakeshore. Easy can fit 2-3 40' Class A or 2-3 30 foot fifth wheels. Big easy turn opening.
The lakeshore is a nice walk about, just keep your eyes open for bears. Kluane is bear country. We've seen them there but haven't ever been bothered by them. Keep a clean campsite.
Another pleasant stop to break up that stretch of drive is Lake Creek gov't campground, near Pickhandle Lake. It is quiet. Subtle. Peaceful. A creek runs nearby, right by some of the sites. We quite like Lake Creek.
Another neat stop is about 30 minutes south of Haines Junction on the Haines Hwy. On the shores of Dezadeash Lake surrounded by mountains. Again, gov't campground so $12 per night. The Haines Road is in excellent driving condition, much nicer than the Alaska Highway.
Across the border in Alaska, take a look at Deadman Lake and Lakeview campgrounds. Both nice stops. Not well suited to very large RVs but we've done both with our truck and 25' fifth wheel.