If you look at the profiles of those making the "mods" I think you'll find most are done on motorhomes 35' and longer. We're on our second Winnebago Adventurer. Our 2001 32V (actually 32' 11") benefitted from an add on rear sway bar and new shocks all around. This was a 20,500 lb. chassis with a 208" wheelbase, and 19.5" tires The shocks on that model were still Ford shocks and only expected to last 25,000 to 30,000 miles. We replaced them with lifetime Bilsteins which now come standard on the F53 chassis. We drove it over 100,000 miles without needing to make any additional changes on the suspension, engine, or transmission.
Our 2013 Adventurer 32H (33' 3") is built on a 22,000 lb. chassis with a 228" wheelbase and 22.5" tires. We haven't made any modifications, nor do we intend to make any. It runs and handles fine.
Many of the motorhomes that have been modified also seem to have the large house built on the shorter wheelbase models of this chassis. Keep in mind there are at least 3 different wheelbase lengths for each weight class in the F53 lineup, except for the 20,500 lb. chassis which only has 2
Here's a link to the 2014 F53 chassis brochure. Note the different wheelbases and tire sizes, (among other things) between the different chassis weight classes
http://www.fleet.ford.com/resources/...2014_LoRes.pdf