I would have kept the liners in the steel frame.
Put some glass/acrylic on the front, cut two holes in the back for intake/out take, hook up a sump, make a top out of an acrylic sheet, add water, cycle, put fish in.
ok its been dug out of its "next to the garage by the fence" hole.. hanging out with bad reverend and nolram got in the way of doing work... but tomorrow work will be done because i am REALLY not happy about the bite marks on my previously flawless arowana