You could make your own as long as you pay attention to details and follow procedures. Talk to an installer as a consultant. Have someone come aboard to give a look see. Look up the needs for the install.
I have known several folk who changed from electric to propane stoves although they paid someone to do it on Tolly's ~ 45'. Although I saw the boats and interior I did not pay a lot of attention to the hows of the doing or where the lockers went.
Consider building another chase for the propane line. It will entail building something but if just the one line it need not be huge. I don't know your boat but can a chase be installed between two windows?