@Dan It rather depends on the allegory. There are the "Rebekah leaving her water jug represents the Christian leaving behind the law/sin/the papacy" type allegories that seem to have no basis in the text. It would seem hard to "show your work" on those.

Personally I think Matthew Miller has a number of good answers along those lines here. Maybe you wouldn't call them allegorical, though.

Peter Leithart, in his book "Deep Exegesis", I think works hard to show work in building out these kind of readings.