Re: Rear rack question!!!!!
I like the seat post mounted racks myself, but they can "swivel" around on you if a heavy enough load is placed on them. I had one on one of my MTB's back when I first started working at Boeing since I needed a way to get me and my tools from one side of the flightline to the other quickly. My tool bag and about 30lb worth of tools was enough to make the rack swing out but a few small steel rods going from the back of the rack to my seat mount bolt was enough to keep it straight.
If you can use a few 5/16" or 3/8" steel rods and bolt one side to the rack and the other either to the axle bolt or the seat mount bolt if you got rear suspension like I did, it will become strong and stable, but still easy to remove and install if you want to take it off when not needed.