Personal preference for me is to make sure both point and flat probe like butter, no matter what the temp is. (Probing trumps desired temp) Depending on the temp I am smoking at determines what IT I begin probing. As far as holding goes I use a Cambro and or a Cambro gobox top loader, which will hold two briskets or 2.5 full size pans. 7 hours is the longest I have held but as in your case you could always put back in your smoker during the latter hours at 140 and keep it warm until serving time. Just my 2 cents and how I would do it.
If your just using foil, towel and a cooler, check it after 4 hours for temp and then use your SM020, it will work great as a holding oven just as it is great as a smoker.