i had the same problem this last rally and we (myself and mostly gus spies) solved
the problem by pushing the thermocouple forward until 1/3 of it was in the flame.
after dark we could see that when the burner lit, it pulled the pilot flame into
the tube and off the thermocouple. the thermocouple sensing less heat thought the
flame was out, and as it was supposed to do, cut the fuel off. my wife was so happy,
she had hot water. good luck, i hope your solution is as easy as mine. Travis