There are no chassis problem associated with the 2001 Diplomat that I know of. That is the coach I own and love it.
If you make the purchase, be sure and raise the front jack BEFORE raising the rear jacks. It has a 3-point jack system. If you do not raise the front jack a little first, the frame may twist just enough to crack a windshield. Easy to prevent.
Make sure the latest Norcold Fridge recall has been done, or get it done before using the fridge. It will not cost you anything, but parts need to be ordered.
2001 Monaco Diplomat 40' PDQ - 08 Honda CR-V