Spare Tire on Roof

[The Ledge]

Folks,

Need to take my parents in addition to my daughter, and 2 of her teammates to a bball tournament this weekend. My H2 has the interior spare tire and was planning on removing it for more comfort and gym bag space for the 2 hour ride on a major highway. I have factory GM roof rack cross bars but was also planning on laying a spare blanket down first, then affixing the spare tire down, cross tied heavily to the crossbars. Am I good to go on this? or am I creating a hazard here without a proper tire specific roof rack? Feedback appreciated from the experienced. Thanks in advance. Ed