While I don't wear 24/7, I have worn 24/7 for stretches of time, up to a week at most and I have only ever gotten a rash about 3 times, which is a pretty low amount considering I have worn on and off for the last 8 years.
My prevention is simple, I use zinc cream, I apply a coat to my bum and I apply some to my groin area, between the legs before I diaper up. I also use corn starch based baby powders as they curb moisture better than the standard stuff. I also make sure to stay well-hydrated.
A lot of the time people get rashes, I believe it's not due to the total time spent in a diaper so much as the potency of their urine. If you drink lots of water and mild fluids like milk, you'll wet, but it'll be inoffensive allowing you to wear for a decent amount of time. Also, goes without saying, if you mess, change immediately, messing runs the greater risk of causing rashes as opposed to wetting.
The zinc cream and powder does really help minimize chances of rash though. Zinc cream is resilient, it'll stick to you long after you change even, that's protection you can count on
Also, zinc cream helps for fending off active rashes. When I had rashes in the past, I put on some zinc cream and it was basically gone overnight.