I've been fighting this since I purchased the Mirada used several years ago.
To date, the idlers have been replaced, the belt has been replaced, and the tensioner has been replaced. This all seems to work for 50-100 miles, then its Chirp-Chirp-Chirp again.
My latest attempt is to install the shortest belt I could get on it, I tried a 108 1/2, but I couldn't get it on. I was able to get a 109 3/8 belt on, but had to remove then re-install the idlers, not a big deal.
I'll need to drive it a few hundred miles to see if this stops the chirp.
Chirp-Chirp-Chirp – Try a smaller belt | 2001 Coachmen Mirada 300QB