Thanks Bob. I did find this info on a MSD ignition page:              ( MSD Ignition Controls are designed to withstand underhood
temperatures but should be mounted away from direct
engine heat sources such as headers or manifolds. The
ignition control can be mounted in most positions except
upside down. Mounting the unit in an enclosed area such
as the glovebox is not recommended. When running, the
housing of the MSD will be hot to the touch.)

I had my Crane CD unit on that apron also and it got very hot as well. I moved it inside the vehicle where the center speaker was under the dash. It seems to run a lot cooler even though it is in a confined space.
 The Crane specs are that it draws up to 9 amps so I suspect it generates a lot of heat on its own, ergo the cooling fins incorporated in the housings extrusion.
 My guess is that the MSD is similar.

I have had the MSD 6A box,  Blaster II coil, and MSD distributor for several years, and the box is mounted in the same exact location. I have only had one issue with that setup and that was failure of the pulse coil in the distributor. Not any problems with the box or the coil.

Ron68 - interesting, my box failed and was repaired by MSD for a nominal cost (less than $50), the pulse coil had also failed and needed replacement.  I found the pulse coil failure after the box had been repaired and the system still didn't function.  Replaced the pulse coil, no problems since.

Thanks for all the replies guys, maybe I am worrying about nothing.