I recently added them to my 07 Seneca. I installed Air Lift 5000 lb bags. The biggest hassle was removing the 1/2" rivets that held the jounce brackets on.
really any truck specialty shop should be able to clue you in on this. Most trucks on road today have air ride. My Brother in law added it to his older MH and is very happy with it. Check some of the off road specialty shops they may be able to direct you also. I think Keldermans (not sure of spelling) is a prime supplier of aftermarket air ride systems. Check their ads in truck magazines diesel power or diesel world.