How do I install horizontal propane tanks in my Lance 1161?

Fixed mounted propane containers for MH , B vans and commercial trucks ,are always ASME tanks . Dot cylinders are considered portable . The regulations for each are different . ASME horizontal tanks built prier to 1998 where exempt from OPD requirements because they could not be retrofitted , and they are built to a much higher standard . Horizontal DOT cylinders where not exempt . As far as I know there is no re-certification requirement for ASME tanks . New ASME tank do come with OPD valves .