The problem really resides with the retailer/dealer--say that quick and it sounds a lot like realtor. And they are a lot alike-to suck the most money out of the deal they cheap-out on the biggest expense which is the installation. Just like good and bad HIs, there are good and bad installers. Manufactured home (nee trailer) installers are now licensed by NY department of state, and this has raised the performance level to some extent-sorta like licensing HIs[:-dunce]. In fact, when an installer applies his seal to a manufactured home, he is certifying the propriety of every system in the home--inluding the on-site work of the electrical service, the gas service, the water service, the foundation structure and on and on. This is backed up by a cash bond for rework that is directly accessible to the NYS DOS. There is no certification needed for installers working on modular homes!! The AHJ needs to get seriously involved in all of these installs in order to improve the conditions you describe. Of course, the majority of my inspection work is a direct result of consumer complaint activity--so let's not fix too quickly[:-tong2]