Where I go hanging here in NSW it's mostly only only down to freezing or a little below, even in mid-winter (like now). With those temps I find my 3-season 2/3 length Yeti UQ (with my HG 20°F TQ) works for me from shoulders to knees. But even with a 12mm (1/2 in) thick CCF footpad, and wearing long johns and possum/merino socks my lower legs and feet get cold in the wee hours.
Rather than getting a second UQ such as a full length or whatever a UQ that reaches from shoulders to feet is called, I thought a snap-on down-filled extension for the Yeti that goes from under the knees and covers around under the footbox of the WBBB would do the job, since I'll only need the extension in the colder months.
Has anyone made or had made such a device? I figure that the extension UQ should have about the same fill and loft as the Yeti, and maybe a draft tube to "seal" the join to the Yeti. The snaps would take care of connecting it to the Yeti, but how could it be connected at the foot end? Maybe a cinch with shock cord?
Any thoughts, advice, or ideas?