My concern has always been transfering a load from a rigid steel plate to the sump fixings, I wonder if that force could damage the block itself (I have had a previous car where sump damage transfered to the block casing around the fixings).
As such I always thought a chassis mounted plate was best, but I am no engineer!
Either way I suspect the risk is lower than that of ripping off the oil filter/drain plug on the later Aeros (Series 1 is remotely housed safely in the wing).
