I store mine in the garage upright (but thats just cause it takes up less room)
when i transport it in the RV, Jeep or Truck, I do so w/ it laying down in the horizontal position & i BLOCK IT IN w/ other items so that it cant roll around.

filling tires - it must be in the UPRIGHT / Vertical position - in the vertical position it can dispense GAS only (not liquid).