Jim,
Just my 2 cents but, I'd rather see you develop a rear skid. Noone can deny they eat up ground clearance (about 1/4 to 1/2 inch) depending on design. But, I think it's just as difficult to deny that they better protect the diff than simple covers. Covers are great on front ends but, skids work better on the rears. And, I'm certain however you'd design it, it'd be better than what's available currently.