My thing with this is that the contact points on the bike be respected. Shoes, gloves, glasses, helmet safety, clothes including bib. They should be perfectly comfortable and functional. If a bib has gotten "tired" at all, I junk it. Even for 90min on the trainer a bib with tired pad is no good. I ride to enjoy myself, not to get saddle sores or a sore bum because I'm too cheap.
I wonder if there's a reason why people don't ride long indoors if they always wear crap old bibs with no support and feel terrible!