I've made 3 road trips to Alaska the past 6 years. It's a fantastic trip with tons of info. available online. Milepost Guide is a must have and an invaluable piece of gear. Even with the most up to date guide it won't be 100% accurate. On my last trip I found 4-5 gas stations closed in BC and Yukon and barely made it to the next gas stop. You have to travel about 500 miles across the Yukon with gas spaced out 100 miles or more, so you really have to plan out your stops. 2-5 gallon cans of gas mounted on the outside of your rig will really help with the gas anxiety.
Do take a full took kit with tire repairs a priority and excellent spare. Plan on at least one flat. The roads are decent for the most part, but depends on the winter and frost heaves. There's always extended areas of road under construction in Canada down to rig shattering washboard and the occasional frost heave that will snag you at the least expected time as you're tooling along at 60 mph. If it's wet and it probably will be early season your rig will be absolutely filthy. If you're a neat freak and worry about a spotless rig Alaska isn't the place to go. Most of the RV parks have washing facilities, so you can clean away if so needed. I'd just wear the dirt as a badge of honor.....:)
Do look up the Cassiar Highway N. BC as an alternate to the most scenic route to Alaska. This highway is now paved the entire length, so you won't have any gravel roads to deal with. Take the side road off the Cassiar (50miles) to Stewart BC and drive into the tiny town of Hyder Alaska. The closest access to Alaska from the lower 48. This is an incredible scenic area with glaciers next to the highway and a cool little funky town. Large bear viewing area just outside of town that's gets very busy once the salmon runs start in July. You could easily spend a week here. Up the road (10 miles) from Hyder you go back into BC and climb your way on good roads to the Salmon Glacier. 2nd largest glacier in Canada, so it's amazing to see. 2-3 RV places in Hyder and more in Stewart next door, so no problem if you want pay camping. Tons of places to park overnight for free throughout BC,Yukon, Alaska, so I wouldn't think you would have any problem finding a place for the night unless it's a holiday weekend.
Everyone goes like hell to Alaska, so if you want to enjoy some wild lonely country spend time in the N. 300 miles of BC and the Yukon. I've done the Robert Campbell Hwy in the Yukon out of Watson Lk (250 miles gravel) and saw maybe 4 vehicles in 10 days. Dozens and dozens of lakes, rivers and creeks. If you're into fishing for grayling or n. pike the fishing is incredible.
The highways in Alaska are in good-excellent condition, but for the most part only go from point A-B, so if you're wanting to do much side road wandering the roads aren't there. June-August is mobbed with RV's, tourists and fishermen,so if that's not a concern Alaska is an excellent destination. Early mid May-June is excellent depending on how much snow, and then mid August-Sept. when the mobs go home. Look up the Old Denali Hwy, Tangle Lakes area out of Paxson Alaska. Another excellent area to spend a week or more if you are heading to Denali. Early in the summer you will be very fortunate to actually see Denali as it's clouded in about 90% of the time.
My next trip this summer will be spent in N. BC-Yukon, I'll save 2,000 miles of driving and see every bit and more that Alaska has to offer without the mobs of people. I found no issues in Canada or Alaska safety wise. Be sure to have proper documents in order going across the border (passport/enhanced DL) and read up on what is allowed. If you decide you need bear spray save yourself the trouble crossing into Canada and buy it when you arrive in Alaska. If you tell the border guard you have bear spray they will pull you over and make you show it to them along with a thorough search. No firearms and know how much alcohol you are allowed to bring in. That will avoid the majority of border trouble. Oh, and if you have pets, have the documentation up to date on rabies etc. If you don't they won't let you cross. Don't ask how I know this!.....:)