I used 100mm (width) x 25mm (thickness) strips, the length of the subframe, scarfing joints where needed. Drilled and tapped the subframe at 300mm centers. Counter-bored the HDPE to 18mm depth, leaving 7mm of material for fastening. With the bolt and washer in place, this results in an approx. 12mm wear before the bolt heads hit the chassis. I also counter-bored for the chassis rivets.
By the looks of your subframe main rails, you could use 50 x 25 strips, and in lieu of drill and tap, counter-bore the mounting holes (just large enough for the drive bit), use 14g metal tec screws secured with sikaflex (these have a 3/8 drive head) plug the counter bore with sikaflex.
If I need to replace it at a later stage, I can use the old strips as a template.