Unfortunately, I have neighbors and a twitchy girlfriend to contend with. Otherwise I would totally try that.
In the meantime I have a bunch of holes to drill.
Should be an interesting experiment. I drilled my chassis (well, FPE did) right from the start, so no A/B comparison available.
Don't forget to vent the bottom! That cool air has to come in somewhere! Mine has a cheese grate bottom on it. Neat stuff cut in various sizes for custom truck grills ... got it offa da bay.
You can bend it too. I cut a couple pieces of scrap 1x4 for the angle I wanted, then just compressed the metal between the two pieces with a couple C clamps. It'll want to spring back a little, so just cut the angle a bit sharper than you want for the final piece.
PS ... I wouldn't lose any sleep over the temps you're seeing. Seems to be pretty much ballpark on a typical amp.