Try using tear away stabilizer underneath. Light weight will work. You'll need to be carful removing it so you don't pull stitches out. If you have a walking foot use that too. I sewed thick slippery items on my DSM using this method.

I don't think I'd use the featherweight for it. They have fairly weak motors compared to most vintage machines.
Did I miss it? I didn't see anything about you possibly loosening the bobbin tension to make it easier for the top thread to pull it up...

My vote is for an older, mechanical machine. I did boat covers and repairs on the cloth top and tonneau covers for our MG. My machine was an Elna Super 62c. I still mourn that machine. I bought it in 1972 - forever ago.

Good luck.

Pat

The nylon thread might be the problem. I could never get the tension right when using it, even on regular quilter's cotton.

Is there anyway you can use a regular polyester thread instead?