No Main Burner in Oven

I have a motorhome with an older Magic Chef LP range. The oven pilot lights and stays on and gets brighter and higher when you turn up the thermostat, but the burner in the oven never lights.
I have checked everything I can think of. I would appreciate any troubleshooting tips you might have.
Gerry (Bryan, TX)

Gerry, assuming the LP pressure is set correctly at 11.0 inches of water column and the unit is relatively clean, here’s what should happen. When you set the oven thermostat to a desired cooking temperature, the standing pilot flame becomes slightly larger, which you have noticed, and begins to heat a thermal bulb attached to a component called the safety valve. This thermal bulb, which is filled with mercury on the older units, expands a bellows in the safety valve and allows the main burner gas to flow from the thermostat to the safety valve and then on to the main burner. As the secondary flame becomes larger, be sure it fully engulfs the thermal bulb. The positioning of the thermal bulb in the secondary pilot flame is crucial. It has to be directly in the fire in order to boil the mercury inside. If it is indeed fully engulfed, the safety valve is probably faulty and needs replacing. Safety valve replacement requires removing the range to gain access to it. And since it can sometimes be a tricky replacement, this one might be best left to the professional technician.