first I would draw the shape, flat. I used a 2pt arc that I then rotated (with copy)
I cut it from peak to valley. that way I know my piece starts and ends horizontal.
mirror + copy as many times as you need.
in your example there are 8 hills and 8 valleys.
clean and weld.
from there, I group the shape, use truebend (free on the extension warehouse), then it’s a simple follow-me.
if you want to adjust the height of the curve, I’d advise to do it before the follow me. simply scale your shape.
then it’s simply a matter of mirror again.
as you see, scaling after the follow me squishes the tube. so be careful.
I used a circle, you could use whatever shape you want.