Welcome to the forum! There has been much discussion of the questions you are asking. Try the search feature, you will be entertained for hours!
Your Vegas is built on a stripped E-450 chassis. Any reference to CHF, cheap handling fix, will not apply. Your handling question prompts the question to you, how much do you want to spend?
The short answer to handling starts with proper inflation (see the sticker by the driver's seat, and the next thing is alignment by a shop equipped for trucks.
We found that the cheap mesh lumbar support helped make the seats bearable. They are about $9 on Amzn. Some have replaced the seats with power units from sites like
www.shop4seats.com
You thought you bought a complete unit, but really it's just a kit! Waiting for you to make it right for you!
Enjoy the journey!