for the tcase one, you need to install nutserts in the crossmember and in the hole on the frame. mine didnt have them.
for the front end skid, you will remove that little plastic thingy thats bolted there and bolt the skid in its place. i think all the hardware is there for that one.
for the gas tank, if you have a hitch you need to remove it to install the skid. they bolt to the same holes. youll get the skid on first, then it gets sandwiched between the hitch and the frame. its kind of a juggling act, definately want 1 or 2 buddys to help you with this one.
Reliability is relative
I had some nutserts for the transfer case skid plate that I gave away on here after I got mine. I bought a lot of them when I did mine. I'm pretty sure they were 10mm nutserts. I can't recall the outer diameter of them though. I actually ended up only using it in the frame rail and used flange bolts and flange nuts in the cross member. I also welded the lip of the nutsert to the frame rail to prevent it from spinning, like the factory ones do when you go to remove the skid plate. Fishing bolts into the frame rail for the gas tank skid will be fun. You'll have to pull the rear bumper cover to access the inside of the frame rails. The first one isn't that hard to get to, but after that, you'll need the help of a flexible magnet.