Hello,
Our Diplomat with 400 ISL has been reasonably good. Replaced the inverter and turbo under warranty. 44,000 miles with no other major maintenance.
Currently upgrading to HD Winegard, flat screen HD and new 200 watt solar.
Eight outboard air bags on chassis are very good for stability.
Best of luck,
Crespro
Crespro 2021 Grand Design 310GK-R, 2020 F250LB, 7.3L, 4.30, Reese 27K