Masonite is a brand name for hardboard.
The problem you will have is that it's very difficult to drive a staple through and it's virtually impossible to get staples short enough.
If you are using Irish Linen the best way I've found is to wrap it around the edges and glue with Aleene's Tacky glue. It's kind of slow going--you have to sort of pull the fabric and press it into the glue, then keep working it until it's pretty dry. The next day you can spritz the cloth with a spray bottle, then dry it with a hair dryer and it will come out nice and tight.
J. Kent Hollingsworth
Vintage system: DB Systems DB-lB/2A Preamp; DB-5 Tone control; DB-9 Headphone amp; Adcom 555/II amp, KLH Eighteen tuner; Tivoli CD; AR-3(a) speakers; AR-91 speakers; VMPS sub; AR-XA Turntable (awaiting restoration).
Home Theater speakers: Cizek KA-1 front; Cizek HTA rear; CSW Ambiance side; Minimus 7 (Zilch mod) front wide; Home brew front high; rbh center; CSW sub.