A little advice. Take your time driving up to Mullen. The drive from I-80 north is awe inspiring. Some of the most beautiful landscape I've ever seen, and it starts about 5 miles north of North Platte. (Apparently, NE-61 is an amazing drive too)
Take in the scenery from your cabin. Enjoy the song of the Western Meadowlark. Enjoy the light show at night (you'll never have seen so many stars). Enjoy the fire by the DR clubhouse.
Drink lots of water, use lots of sunscreen, and have fun!!!