Mmm...Not sure about that if you refer to Mx5 ones.
TBH, owning 2 for 15 years as we do, never had issues with rear discs...but there is a reason in my opinion & experience.
In our cars, frankly rear discs are superfluous. Quality drums would be fine...but would look krap and "unsporting" They do little braking effort work (about 20/25%) and don't like being ignored. I've always clicked the handbrake up when safe & in the dry every other week to get them shiny & toasty like the fronts, and lubed the sliders etc. People in the OC Club have scoffed at this theory. They are usually the ones who suffer jammed calipers & rusty inner discs, whereas my Mk1 rears are fine at 146,00 miles, and I only had to renew our 2002 Sport's last year at 98,000 miles. And that is in a car whose rear discs....are bigger than the fronts!
It was a tip I picked up years back from a guy ( engineer) in the Monza OC.