Had a 2000 Rexhall Rose Air for 13 years. 130k miles engine spit a plug, but after valve job during plug fix the compression tested near new. Use synthetic oil and trans. Rexhall builds like a tank, which reduces the cargo capacity compared to some others. I visited 5 factories before purchasing and Rexhall build was far better than the others. Rexhall also stretches the chassis on the 20,500 chassis so the MH has a better wheelbase to length ratio, which shows up as better control on the road.
However, as others have posted, on this age coach condition should be the primary consideration. Many 15-18 year old coaches are near junk, but those that have been cared for have a great bang for the buck.