I clean mine with Megs APC+ then treated with Megs Engine Kote as it dries hard and not a "dressing" per say.. more of a wax. In fact if you smell it, it smells like floor wax!
Tried EK in the engine area, and even with a high volume spray, it still put out small white beads, which I had to spread with a foam paint brush. Now, I just use 303 in the engine area for all plastic/rubber and EK on metal parts by foam brush.
For undercarriage, EK works very well! Wheel wells too!
Regards,
Deanski