It is my experience that many (90%) rv parts are universal throughout the rv industry for appliances, plumbing, hvac, molding, windows, exterior trim, seals, etc. I have bought many parts at pplmotorhomes.com and have have good experiences. You may have no choice but to go through a dealer some brand specific items such as cabinetry, inside furnishings, decor, etc.
2010 Keystone Outback Sydney 5'er
2012 Chevy Silverado 1 ton, LTZ, Standard bed, Crew, 6.0 Gasser, 4:10 gears