Product review (5 stars): Great product for a great price
Perfect for wall mounting a 3 prong 30 amp 240 outlet.  I actually used it with a generator extension cord so I can run my water heater in a power outage.

The package includes some 3/4 inch long screws that you could use to mount the unit to plywood.  Also, it brings cable clamping mechanism to bring in and secure a large cable, such as SOOW cable via the bottom punch out hole.  I used 10/4 SOOW, however, 8/4 would have fit no problem.  Might even be able to get 6/4 in there.

The backplate has a pre-tapped ground screw hole, and suitable for use with a pigtail.  The terminations for the hots and neutral feel very robust and secure.  Plenty of room for 10 gauge wire.  Probably can fit up to 6 gauge.  Plenty of room inside to bend wire and make it all fit without struggle.  This does make the overall size a bit large, but this was not a con for me.  When its all put together, it does feel fairly solid, even for extension cord use.  I would not abuse it, though.  It is not that tough.  Also, this is not water proof at all.  I did not expect that it was, so it is not a con.

I have installed dozens of these over the years.  I think this one is the best.  Also, it is the cheapest, includes the clamp, and easiest to fit the wires inside.  The only downside is that it is larger than others, although not much larger.  If its in the utility room, you are probably not going to care.