I've mounted a variety of open frame linear supplies in a "screw cover pull box". Those are sold by supply companies that cater to the electricians. Hoffman seems to be the most common brand; I've even found a small selection at some Home Depots, but electrical supply houses typically have a wider choice in sizes. And there are a LOT of sizes.
What you want are the boxes WITHOUT knockouts for conduit fittings.
I'll see if I can attach a JPG of a couple units I built awhile back.
Bri