I have read many threads here about upgrades to WH line. I have the 2006 Itasca Model 35U with 12000 miles. After all the reading...I have selectively added:
a. Taylor Extreme SP wires. Wow...very noticeable smooth and even engine acceleration. No more slight hestitations...as it went through gears. Easy to change out through fender well and dog house.
b. Centramatic Wheel Balance System. Installed first set (600 Series) on steer tires. MH rides and feels like it's on velvet. http://www.centramatic.com/
c. Doghouse Insulation. Cut engine and tranny sound 30-40% along with summer engine heat and winter cold. Easy to self install.
d. K & N Filter to stock intake. I've used K & N filters for past 7 years in my Ford trucks. I have also done the cleaning and reoil on them. Here lies the biggest issue..reoiling the filter so as not to gum up the intake MAP sensor. Just follow the K & N instructions and you won't over oil.
e. 100% Nitrogen (N) in all tires. I've used 100% N for 5 years in two trucks and one 35 foot FW....and virtually eliminated major tire heat failures...and frequent pressure service checks. Last trip I took in my Itasca...three weeks..3800 miles needed only one pound of N to each tire.