I think way too much to answer with so little background. A lived in trailer could be pretty worn down. I have replaced both AC units on my trailer that gets at most 60 days a year and usually closer to 45, and mine is a 2019. Suspension has been replaced and repaired twice. One slide out motor and gearbox replaced and one slide out motor ripped itself off the wall. Sofa "pleather" has all started cracking in the past year or so. Both fresh water storage tanks have cracked and needed to be repaired, I would be surprised if all the cheap plumbing could hold up to 10 years of constantly pressurized pipes and if doors and screens, windows were still in alignment.
As for the truck, without knowing the major maintenance history I would be very nervous. If all routine maintenance has been done including fluid changes I would feel better but at that mileage you likely need new injectors, possibly fuel pump and tranny is getting near the end too. Again, if current owner was on top of maintenance you could be okay. Yes, diesel engines can go several hundred thousand miles but require regular and expensive maintenance.
Bottom line, get some more history if at all possible.
My two cents anyway.