Yes, that is the correct material.  I replaced ours last year and got it on EBay for 14.55 and free shipping.  Looked at Amazon but find Amazon is almost always more expensive than EBay + on EBay it is always free shipping, Amazon you pay extra for shipping unless you pay to get Amazon Prime.

Also replaced all the screws with 1" stainless steel.  Our 177 was 10 years old when they were replaced.  The worst screws were the ones underneath that run from front to back.  Over half of them were totally rusted away; had to re-drill new holes.  Used dicor over the old rusted-away screws and also dipped the tip of the new screws into the dicor before installation.  Took the better part of the day to do the 200 screws.  I did not replace the top 1/2 of the screws on the slide, they were still shiny and appeared like they were brand new, but I ended up replacing the white vinyl insert as the old stuff had shrunk and was beginning to crack.

The vinyl insert I used was called Heavy Duty Insert Trim by RV designer (www.rvdesigner.com) in a 100' roll.  Part number was # E461 (heavy duty white) and your number will obviously be different since you are looking for black trim.

By the time I did both rails from front to back (on top) and all the vinyl insert on the slide I had about 16 - 20 feet left over.