I believe MO2500 has the best understanding on skids as to people who have posted about this so far with the UCF skid being the best example. Danno, the angle you mounted to front of the skid will add a lot of reinforcement but is opposition-ally mounted to how the angle's strength works in the real world. It will work great for what you want, it just isnt the best way to use the angle's strength. Also, the flat spot on the skid is not the problem, it is the lack of x/y support and with it being flat, oviously there is no z axis support. Look at the ucf skid. The 3/4" drop down around the perimeter gives it the x and y support which will pretty much stop it from fully flexing out shape but the depth is where is matters most. The depth gives it the rigidity. And the cross member that they add (small C channel) is mounted with the open side facing downward which puts the "webs" of the C vertical tension which adds more strength (not a bunch when taking about the whole overall skid) and serves as a mounting point. If you give the skid properties that will allow it not to move, then it doesnt matter about the flat spots (as long as they are thick enough to not be penitrated).
You skid will work great, but if you wanted flat and bulletproof something with a full square of angle just inside of the frame rails would be a ton more strong than lined with angles on the front, back and going across like in the second picture of post 980. In that skid, there is not enough front to back rigidity (or along the y axis).
Like sunny's sig says, if it is worth doing, it's worth over doing.
87 MJ Chief in pieces
Bought/Wheeled/Sold: 85 CJ, 79 FSJ, 05 LJ, 06 WK