I completed my hitch job this morning, and as on other forums, I will offer some advice for the DIY person. This is intended to supplement the install instructions from the vendor. My product was the Curt 14137 with Class II rating. Other models and mfg should be quite similar.
Prelim: Car needs to be cold, as you will be working on and above the exhaust system. Jack the car, and support with jack stands, or use drive up ramps to gain access to the rear of the car. Never work under a car with only a trolley or bottle jack!
Once up in the air and supported, let the car cool for a while, until the mufflers are cool to the touch.
Tools(min): Jack, jack stands or ramps, 14mm socket/ratchet, 14mm wrench, 3/4" six point 1/2" drive socket, long 1/2" drive extension, 1/2" drive torque wrench, medium file, rat tail(round) file, or small dremel or angle type grinder.
1. Locate the two rubber hangers for the mufflers. One is forward and near the top, one is rearward, and near the bottom. Pry off the bottom rear rubber hanger from the round stanchion on each side. Leave the top one alone.
2. Using the 14mm tools, remove the two nuts from each muffler connection flange to the exhaust pipe, set the nuts and bolts aside. If the gaskets are secure on one flange, leave them where they are, and do not damage them, they can be re-used.
3. Pull and separate the exhaust pipe from the muffler flange and swing the muffler down, and toward the outside of the car. It will remain hanging on the upper rubber hanger, and be out of the way. Do this on both sides, and leave the mufflers hanging to the side. If you need more clearance, you can remove the rubber hanger just forward of the rear driveshaft, but I didn't think it was necessary.
4. You will now have good visual access to the chassis rails where the hitch will mount. Note there are three rubber plugs in that chassis rail on each side. Leave the most rear one, and remove the center, and forward(larger) rubber plugs. Do NOT remove the muffler heat shield.
5. Test fit your hitch up into place, and make sure the holes and cutouts for the hitch align well with the holes in the chassis where the plugs were removed. This test confirms you have the right hitch, and gives you an idea where the unit will sit.
6. The front large hole needs to be made just slightly wider, and the rear hole enlarged slightly for the bolts to fit through. If you have a smaller hitch, or one with a lower rating, this step may not be necessary. Check that the bolt head will fit through the large hole forward, and that the metal retention strap will also fit through. On my hitch the bolt head was slightly larger than the front hole, and needed modification.
6a. Using your file, or dremel or grinder, remove a notch of metal on the left and right chassis rails to accommodate both the bolt head, and the metal retention strap that came with your kit. Both pieces will later need to go up into the chassis rails. Careful you don't push them all the way through, or you'll have to get a magnet and go fish for them. Don't over-grind up there, just barely enough so the hardware will fit through the front hole and stay up in the chassis rail.
7. Using the rat tail file, or the grinder, enlarge the rear hole slightly so that the shank of the bolt will fit through. Do not notch this hole for the retention strap, it will be fed through with the fishwire kit and remain above the hole.
8. If you have not used the fishwire technique, watch this video:
If you have done this before, start the fishwire bolt, and retention strap from the front slotted large hole, and guide the fishwire rearward, and draw it through the rear hole. Stuff the retention strap up in the chassis rail, and then the bolt up in the rail, and draw them out the rear hole with the fishwire. Don't stuff the parts up into the chassis until the fishwire end has been pulled down through the rear hole, or you will lose the whole asm. Leave the fishwire on the bolt threads for now.
9. Do the same on the other side of the chassis rail, you now have two bolts, and straps hanging down from the rear holes.
10. Use the reverse fishwire technique to push the bolts and straps up into the front holes on each side. You now have four bolts in the chassis rails, and are ready to put the hitch up in the chassis. Remove the fishwire from the left rear bolt, this will be the one you start with.
11. The hitch is aft-heavy, so start with the rear bolt to take most of the weight off your chest. If you have a helper, now is the time for them to stand at the rear of the car, and hold the receiver end while the hitch is moved into place. Lift the left rear, and slide the rear hitch flange hole over the bolt being careful that you do NOT push the bolt back up into the chassis rail and lose it. With the hitch flange over the bolt, put the nut on finger tight several threads, but do not tighten it up. Note the fishwires on the other bolts will interfere with the hitch asm a bit.
12. Move to the right side, and thread the rear fishwire through from top to bottom(downward) hitch asm rear mounting hole. This will help guide the hitch up into place, and protect it from getting pushed up into the chassis when the hitch is raised. Tip the hitch up in the rear, so the front bolts are not in the hitch flange yet. Put the right side hitch up, and thread the bolt and fishwire through the flange. Remove the fishwire now, and thread the nut on finger tight.
13. Now guide the fishwire for both front bolts through the hitch flange front holes/slots going top to bottom again. The hitch will now hang in place, and remove the front bolt fishwire, and thread the nuts on finger tight.
14. Use the 3/4" socket, extension, and torque wrench to tighten in a cross pattern to the stated torque rating on the instruction sheet. (if you have a ratchet, you can snug them up and finish with the torque wrench).
15. Swing each muffler inward and upward, and mate the flange to the exhaust pipe. Be careful of the gasket. If you damage it, you'll be making a trip to O'Reilly's. Push the 14mm bolts through the flanges and gasket, and put the nuts on finger tight.
16. Use a little lube, and put the lower rear hanger rubber snubs back on the hanger shaft of the chassis.
17. Using the 14mm socket/ratchet, and wrench, snug the nuts back up.
18. Wiggle the exhaust pipe, and muffler as a group side-to-side, and make sure you don't hear any rattling, or clanging. If you do, you'll regret leaving it like that later. If you hear any weird noises, investigate them now. Insure the front exhaust pipe hanger is attached if you removed it earlier.
You're done! Now, go tow something!
First pic: chassis rail mount location.
Second pic: Muffler swung down and hanging from the upper hanger.