Chicken – How to keep chicken juices in the chicken when cooking in the oven

The technique you describe is pretty much just the standard way of roasting a chicken. A V-shaped roasting rack is excellent for this purpose. As for keeping it moist, the standard technique is to brine the chicken first. Done properly, brining a chicken results in a moist, tender bird with crisp skin, and doesn't involve adding any additional fat. I normally brine by putting the chicken in a stew pot, covering it with cold water, adding about a cup of kosher salt, and letting it sit for 90 minutes.

Without a reference to the specific product, I would assume that it is in fact flour.

It's very common for many chicken (and other meat) recipes to call for dredging in either seasoned flour, or flour followed by an egg wash and spice/breadcrumb mix. Since these commercial mixes obviously have to be completely dry, they are most likely to be seasoned flour.

Check out some recipes for seasoned flour (alternatively called seasoning flour), you'll probably find them to be very similar to the mixes you've been using.