What's different in the van setup at night? Do you set up a bed for example? Do you inadvertently block the return air path or warm air discharge path?
If it is not that then you should probably have it checked by an RV Service dept. I looked at a service manual and found:
6. Customer complains of unit going into lockout only once in a while:
But the troubleshooting steps are technical - checking electrode, burner, gas pressure etc. the module is mentioned also.