It is wise to not use the highway shoulders regardless of how solid they look from the driver's seat.
Soft shoulders are all along the Alaska Highway. Unless you see other tire tracks on the shoulder (meaning it is likely a popular photo stop), don't pull your RV onto the shoulder. Even then, be careful...where I pull off with my little car might not take the weight of your rig.
I see a handful of RVs tipping well into the ditch each summer on my drives between Whitehorse and my place west of Whitehorse. This year also seeing a fair number of trailers with axle and tire problems. Usually leaving the trailer behind with a tire or two off then driving into Whitehorse for repair.