I agree that 3mm alu will get eaten up, but there seems to be plenty of space around the wheels with those chunky hdpe sidings, and they will no doubt get chewed up, but will keep most things out.

I would be tempted to cover the top in hdpe (maybe with a couple of extra little sheets to box in the radio gear and battery underneath the top sheet) and keep the front plates as is with possibly some extra hdpe to wall off the motors from the front plates (just in case)... all depends what you can get away with if your needing to save weight, but maybe changing some of it to hdpe would help with this?