Thanks! I did block off the grills w/ some homemade closed-cell foam inserts last winter, and they definitely made a noticeable difference in engine warmup time, cabin heating performance, and mileage.
Main issue here though (KS), is that the temperatures can often swing so wildly from week-to-week (or even day-to-day), especially in fall and spring -- i.e. imagine 85 F+ temps for couple days, then down to 20 F or lower over next few, and then back up to high temps again right after that, and so on... This requires repeated removal and replacement of some (or all) of the foam grill inserts, such that it gets to be bit of a bother.
Those grill covers you used to offer (ID Parts) look a LOT handier and easier to swap in and out, whenever necessary. So yes, please do let me know if and when they become available again -- I am DEFINITELY interested in them. Thanks again!