The PL around the Speakon is a good idea, though if the jack ever went bad (highly unlikely), you'd have to cut the whole thing out. I am in the same boat with the 4 OTops I'm building. I didn't want to deal with having to recess the big jack plate and spending the additional money on it, and just went with countersunk holes like this:
However, the screws I have for the Speakons are the proper #4 size and they are 1/2" long, so they will get a very sold bite on the mounting location. Should be just fine.
So I guess I've got to think about possibly PLing mine in as well. The plan was to just put bathtub silicone on the inside of the panel, all around the jack. That would seal it up and give some additional holding strength. I might go with that and see what happens. Worse comes to worst, I wind up cutting a hole for a proper jack plate.
*edit*
Now that I think about it, I can't remember offhand what the diameter is on the countersunk hole in this pic. The outer flange of the round, flange-type Speakon is 2.0"
http://www.neutrik.com/zoolu-website/me ... ing+NL4MPR
If the hole I cut is at least 2.25" (the inner hole is not exactly centered on all the cutouts, so I need wiggle room), I may go ahead and order the round type. I'm already about $150 over budget, so what's another $25? If the cutout is only 2.0", I'm not going to worry about it.