Distance wise it's the same if you go to I-15 or SE to 89 by way of 59/389 to Bryce, BUT it puts you close enough (30 miles) to go to Jacob's Lake and the N Rim. Stay at the USFS CG there or the private CG and use the Jeep to go the 40 miles to the N Rim.
Are you staying at the KOA or Kodachrome Basin State Park in Cannonville?
I would recommend doing some of 12 in the Jeep before deciding on using it to get to 24 in the MH. From Cannonville it's 17 miles further to use 22 north from Bryce (nice level two land road) and 62 to 24 and then 24 to Torrey and Cap Reef NP.