I did something like that on my caravan.Couldnt find a firewall hole at all.I went through the fender,and down the door jamb to a grommet in the door frame.actually worked out nicely...the grommet went right into the interior trim piece,and all the way to the back.
I get alot of shitty installs that come in for insurance claims... see shit like that all the time. Nothing was as good as the kid who had his power wire duct taped to his battery terminal.... "it just wouldn't fit!"