By all means, take a detour north of Duluth at least as far as Grand Marais. Stop and enjoy all the wonderful state parks with their waterfalls and trails, the Palisade Head overlook of Superior, the lighthouse at Split Rock, and Artist's Point at Grand Marais.
Of course, Glacier NP is smack-dab in your path so you ought to spend some time around there, too. Plan on seeing plenty of wildlife. I stayed at the private Glacier RV Park a couple miles west of the W entrance, but for dry camping Apgar is nice too if they have a space. MacDonald Lake is pretty, the wildflowers should be abundant, and the hike to Avalanche Lake is pleasant if you are up to the steady 2.5 mile uphill trail. You can't take a trailer over the Sun Road, but it's worth the drive. Take the Escape around the S end of the park. More good scenery and CGs on the east side, too.