Comfort depends upon the quality of construction. Our first MH was a Coachmen and we did have to run the house A/C during summer heat. Our current MH is a Newmar and we have never had to run the house A/C during summer. We traveled coast to coast with both. The current MH dash A/C keeps the interior comfortable while traveling.
When we built our home I had excessive amount of insulation installed, 18" in attic. With a total electric home and three bay shop with woodworking and welding shop included our electric bill is $140 a month. When one cheap out on insulation they will pay for it in increased heating and cooling bills.
Little to no insulation is one way that motorhome manufacturers cut corners due to no one being able to verify until it is too late. We discovered that the Coachmen we owned had no insulation behind many of the cabinets.