You've got an interesting idea, but I think you're going to work on your proof of concept. Having been the Director of Manufacturing Engineering for Groen in Jackson, MS, I know a little bit about how a steam jacketed kettle works.
Before I get into it, I'll preface my comments by saying that I may not fully understand what you plan to do or what you plan to cook during the winter, so my post may be worthless.
First of all, most kettles are not double-walled all the way up to the lip of the kettle. In most cases, it's only the bottom half of the kettle that is double-walled. If your kettle is constructed that way and you drill holes four inches above your food line, you'll also be above your double-walled portion of the kettle.
If your kettle is indeed double-walled all the way to the top, you'll still have some engineering problems to solve. If you're going to release steam into the cooking chamber, how do you plan to handle the supply side of the source of the steam, which obviously is water? If you're producing steam that's released into the atmosphere, the water must be replaced, but it must be controlled so that you don't force water up the inside of the kettle and out the steam vent holes you drilled into the inner wall of the kettle. This can be accomplished with a valve between your steam generator and your kettle,
if you had an external boiler to produce the steam. Because you plan to produce the steam by means of a heat source under the kettle, you've got a whole different kettle of fish, and keeping your water supply at a workable level could be problematic.
If you release the steam into the cooking chamber, that means you no longer have a pressure vessel and the result will be that you will only be reaching a temperature of 212 degrees within the jacketed portion of the kettle. The reason a steam-jacketed kettle works so well is because the steam under pressure reaches much higher temperatures than 212 degrees. By drilling holes into the inner wall, you no longer have a pressure vessel and the water in the lower portion of the kettle will actually then serve as an insulator and prevent you from reaching temperatures much higher than 212 degrees. You'll pretty much end up with a big "double boiler". I don't know what you're planning on cooking in this "winter version", but if you don't need real high temperatures, you may be OK.
Unfortunately, the laws of thermodynamics may keep you from doing exactly what you hope to do.
If I've misunderstood your intent and purpose, I apologize for wasting space on this thread. ;)
<message edited by jman on Tue, 06/23/09 7:47 AM>