I'm on my second Keystone product. Both have been good campers. It' not uncommon for someone to own a travel trailer for 20 (plus) years. As stated above, it all depends upon your attention to detail to maintain them. Even a multi-million dollar motor home will become trash in 1 year if they are not maintained.
Passports are a pretty decent camper for their price. If you purchase new, you'll discover most warranty issues within the first or second camp-out. If new, warranty will cover everything for at least the first year. If issues develop after the first year, it will probably me minor. After about 5 years you can expect some small issues, like screws, sealing the roof, maybe even some trim inside coming loose.
By 10 years, depending upon usage, you can expect the appliances to begin to show signs of fatigue. BUT not always though! And if something like the refrigerator goes out, there's nothing that could have been done to prevent that anyway. RV appliances are pretty stout, and no reason why they cannot last for 20 plus years also.
Electronics (like microwaves), fail usually after about 5 years. But even in your home, they usually don't last more than 5 years either. And no doubt you'll go through couple televisions in 20 plus years, especially if technology continues to change and evolve.
If you are attentive to getting the wheel bearing packed every year to 2 years, watch for frame fatigue, and spot paint the frame and any painted parts, structurally, they should last forever.
But there again, they are a trailer. They do get dragged over the road. They are exposed to all kinds of weather. And just like your car or truck, if left outside in the weather 24x7x365, you can expect paint to fade, decals to fade and maybe curl up a bit, and rust to form in places you never expected. This is all normal wear and tear, even if the camper never moves.
Even if you park the camper under a roof, humidity will form on the outside of the camper, and anything is now subject to rust... just like a car or truck. Some things are just inevitable. But here again, with attention to detail, there is no reason why a "Passport" should not still be in good service 20 (plus) years from now.
(But you know.... more than likely ... after 2-3 years ... you'll be trading for a different floor plan!) Don't be surprised! Not because of deficiencies in the camper, but because your needs will change and you'll learn what you do not like about the floor plan of the Passport you are considering.... just don't be surprised. I don't know of anyone that purchased their first (and only) camper and held on to it for 20 plus years!
Good luck and I'll give the Passport 2 thumbs up! (And 2 thumbs up on the potential new owner who will take great care of it!)