Below Miles are off of MTB project
Not sure what you are stashing, water? Food?
Rabbit valley, ~ 20 miles, easy access right off I-70
Westwater, ~ 40 miles, paved road easy access (maybe stash under railroad bridge)
Not sure if water works at westwater, you could look into that.
Cisco Pump House Rd & Koko ~ 54 miles, easy access
Dewey Bridge ~ 74 miles, easy access or back around 64 miles where you cross 128
Might be better there a lot less people
Filter water just before 94.6 miles in creek (if it's running)
La Sal mtn loop rd ~ 115.7 miles, paved road, easy access or anywhere from there to Upper Porcupine TH 123.9 mile, 99% paved and good gravel section around TR.
I've done it the way the GPS track has it taking Sand Flats rd. That being said, lots of people take the upper porcupine singletrack down to 128 then into town. Not sure I'd do it with a loaded bike, but I'm old...
Lots of driving, but could hit most of them in a day and with 2WD vehicle. Not sure you would need to hit all of the above just giving you some thoughts.
I did a trip last year in Cedar Mesa area and I stashed some water (2 gallons) buried in sand and something got in there and ripped them open. Maybe a coyote, not sure.
MTB Project Kokopelli
https://www.mtbproject.com/trail/221567