I think you'll be pushing it lol.
I know that Seasonic manufactured PSU's for Antec's Earthwatts series but I don't know what models this extended to, i.e. whether it was the complete range or only those above a certain wattage. I believe these have a different cooling design / arrangment too - that is, there's a rear fan but no bottom fan? Won't this be a problem as outlined in your initial post?