ROC-PRO 700

I’m trying to set up my old guitar amp for harmonica.(too poor to buy any new equipment, gotta run with what I got) Any thoughts on whether closing in the back of this amp would help or hinder my anti-feedback efforts? Any feedback (get it?) on using this amp would be appreciated!

Maybe this will help (in case no one ever heard of a Roc- Pro) Fender, hybrid, open back, 70 watt, single tube preamp, solid state power amp