2 years ago 4 of us were in Alaska for some military training. We had a weekend off and rented some 800GS Adventures. Did 900 miles in a weekend. From Fairbanks to Valdez and across the Denali Highway. Had an absolute blast. We rented from a Alaskan Adventure Riders in Fairbanks. I would not recommend renting from them. The guy claimed we did a lot of off roading (we didn't do any) and charged our credit cards several hundred dollars each for repairs a couple of days later. He claimed his mechanic told him that there was a lot wrong with the bikes. We talked to his mechanic and AAR was lying to us about the repairs. Disputed the charges with our credit card companies and got our money back.
I just bought a 2006 R1200GS Adventure to make a trip up to Purdhoe Bay. Right now we're planning on summer 2018 for the trip as some of our group will be deployed next summer. From Wisconsin I'm thinking of heading up to Winnipeg, head west to BC and north to AK. On the return trip head into Montana and make our way east through the bad lands of South Dakota. It's been fun looking at all the information out there about the adventure north.
I rode up to Deadhorse 2 years back on my then DR650 and I'm glad I took that bike. The road gets slick as snot on some parts, and if there is any moisture, it will build up concretions on your bike. My header never recovered from the trip - always looked rusty. I don't know if there is something you can pre-apply to your bike before you go to keep that nastiness from sticking, but I would advise it. See pic for how my bike looked on return trip. I don't know that I'd want to take my GS on the trip without doing something to protect the bike...
That being said - it was a great trip, one I would be glad to do again. Bring mosquito repellant if you go early-mid season. I went late September and the mosquitos weren't too bad. Call ahead and get what info you need to send them - they have to do a background check on you if you want to go up to the Arctic Ocean/Prudhoe bay, it's a secure area (due to the rigs/pipeline).
You'll pass some awesome scenery and lots of mean semi trucks - oh, they're polite and will wave etc - but they throw ROCKS! One cracked my windscreen nearly top to bottom, it was huge! Have something to protect your paint/glass/lexan (a couple of layers of painters tape works pretty well). And gas in Coldfoot/Deadhorse was over $5.50/gal. Made me glad I was on a motorcycle!
Have a great trip, yourself!