Over 20 years for us with 7 different trailers: bumbper pull X 4 and now on our 3rd fifth wheel, I won't go previous to the tent era.
Lots of simple issues from dead batteries, light bulbs, black tank valve, slide issue, tire, awning, etc. big deal was bent springs, and as recently as this week, A/C blew its factory charge crimp. Installed a valve and up and running. Ours, some of becasue of weather and life, But all in all lots of ours have been normal. Knock on wood, if there is real wood anywhere, never had to replace anything major. How many issues are due to lack of maintenance or non use due to storage: HMMMMM