On a car, you can push on the fender and see if it bobbs, Its hard to do this on a MH.
If I was going to guess, I'd say 5-7 years.
I've replaced shocks on two of my MHs in the past few years.
- I replaced them 2 years ago . They were originals and were completely gone, no compression at all, just a steel rod moving up and down. Other than the CHF, this is the most significant improvement I did in handling
- I just replaced these a month ago. They were also original with original Bilstiens in the front. They were worn badly, a little compression, but nothing like the new shocks.
I used Monroes on the Mirada, and KBYs on the Southwind.