Basic: note Doug's pictures..
Roll and snap closure, Vs. a drawstring to enclose the load and then a waterproof lid over that .

Strap center snap on roller can engage end snap on rack pack, laid crossways.. Packer version, not so.

I have 2 different fronts, the Older Sport-packer, has changed since then.
[Rollers remain unchanged]

lost the girth straps, and the D rings on the buckle straps on the lid..

you will see on the Company website, the horse packer,
they changed how the older bag is used, but still use the basic design.