I’m going to apply it onto furniture of different lengths, so hopefully it’s either at least, say, 6 feet long or it’s something I can make copies of to make longer as needed.

If I needed to use it as 3D geometry I would model it using the method I’ve shown before to model screw threads. In this case it would be 3-strand rope. Then I’d cut it in half.

Do you have to have it as molding that is flat on the back?

Making it in short sections would be a good idea. According to the website you linked to, the pitch of the 1 in. wide version is 1.06" Since it’s to look like 3-strand rope, the pitch of the helix would be 3.18 and to make it look right if you use multiple copies, you need to choose a length that is some multiple of 3.18. Hide the end faces and their edges to make it appear as a continuous run.

An alternative for modeling the 3-strand rope would be to use Helix along path from Sketchucation. This is a quickie. Considerably rougher than my previous example and I didn’t cut the ends yet.