What safety precaution must be taken when transporting propane cylinders used for heating thermoplastic kettles on public highways?

1. Transport cylinders lying flat on their sides in an enclosed truck bed.
2. Store cylinders inside the driver compartment with windows rolled up tight and sealed.
3. Heat cylinders with a torch prior to driving to maintain tank pressure.
4. Secure cylinders vertically in well-ventilated racks with safety caps installed.