Hi Jon,
So, for those who don't or didn't know, there are two straps that go from on top of the windshield over the three bows and attach to footman loops on the outside of the rear armor. this helps support and removes some of the sag between the bows. These straps are used on all M2 and M3 variant halftracks. To answer your question Jon there are two footman loops on the outside of the armor to attach the straps to, circled in red. The footman loops circled in yellow should be on the inside. This is a mistake I see on many M2 halftracks. These footman loops actually have special straps that can hold either 30 cal. ammo cans or water cans. The straps, both top and the five on the bottom, can be purchased at Weebee Webbing,
http://www.odcloth.com/products.html.

The bottom image is of a Scoutcar and it's top and related straps. This is in the M2 Base Shop Data Book. Instead of reinventing the wheel for each manual they reused some images from the Scoutcar manual as they are the same.

Hope this helps.
Steve A.