I only had my '99/'00 RT D190V & '01/'02 C190P with manual-light reefers for a few years total, but can't recall any real issue with the flame going out when driving on LP. It took me a little while on the first one to figure out that it worked best if I'd keep the gas button pushed 'in' until the red needle stabilized, and then 20-30 seconds beyond. Releasing it too soon led to disappointment and another try.
Once, the Tiger's auto-ignition 3-way wouldn't light on LP when I got to a CG at dark... dirty ignitor, or gapped wrong. I was able to remove the flame cover, and use a barbecue lighter to light it. It required moving darn briskly to push the 'On' button inside, then get outside & use the lighter while the LP was still flowing during the ignition cycle, tho'.
Jim, "Why do they lock gas station restrooms? Are they afraid someone will sneak in and clean them?"