HJL,
Belated welcome, sir. I just got finished reading the post and most recent replies regarding heating in an OP/LP, after a fairly lengthy absence. I find I feel the need to remind all and sundry, including my fellow veterans, of the fact that by its very nature and definition, an OP suffers one major distinction from all the other forms of positions spoken of. That is this: An Observation and Listening Post is an outside-the-wire position. It’s not a “defensive line” or “fortified perimeter” fighting position. That means a proper OP is not fortified or improved, as described. Ever. The OP is a “very hasty” or “extreme hasty” at most, and is in fact supposed to be temporary as well, for OPSEC reasons; thus, no hole to begin with. In other words, your OP should not stay in one place for too long; it should be set and camouflaged in such a way as to be within concealment, but able to be moved, and/or abandoned without leaving trace behind at a moment’s notice, once hostile movement-to-contact has been verified. (I reference your own duck blind analogy, but using local natural materials to conceal it.) These mission requirements do not allow for such improvements as have been mentioned. Further, an OP is subject to all four tactical disciplines to a much higher degree than a main line fighting hole; those being sound, light, motion, and trace. Heat signature, and the smell of both the hot bucket and the burning material or chemicals reacting to produce heat will be dead giveaways to your position. Thus, the short interval for rotating the troops manning it; you don’t want them out long enough to get cold enough to need such measures.
When you go putting in a wood floor, logs, or whatnot around the berm so you can mount a roof and so on, you have changed the nature of the position in question from a “sneak and peek” position to a position intended to be defended in place. It becomes an improved fighting position, in other words. I realize SOP and general practices in the field have changed since my days in the Marine Corps, but I am very certain that the intended mission of the OP has not. The only so called OP I have ever seen personally that was modified in any of the ways mentioned was on the “Z”, in Korea, and had been there literally since the ’53 cease fire. For the record, the position in question, even then, was not referred to as an OP, but as a checkpoint. The heating methods mentioned might be used in more permanent fighting positions on the line but even then should be employed exceedingly sparingly, and only in the nastiest of conditions, such as a full-on whiteout, for example. This subject is one of the reasons that troops are rotated on a watch schedule, so they’re not in the holes or on the line for too long, except when absolutely required to defend a set of positions. The rotation for an OP, as it was practiced when I was a young Marine, was about one-third the time of the rest of the perimeter, in such conditions, but that was near thirty years ago. I frankly can’t see where that would have changed very much, but it is possible.
I’m afraid the correct answer for heating a properly employed OP is… you don’t. Semper Fi – J.H.