Same one as I use. Go to the plumbing dept and grab a length of spongey pipe insulation and wire ties. Cut the insulation lengthwise and attach to front/back of the platform.
I'd start w/ vacuum, an all purpose cleaner followed by metal (alum safe obviously) polish on a stiff toothbrush (to get in and around the rubber nubs) and then re-evaluate if more is needed.
I just mix up a gallon of water w/ 2x the normal ONR rinse less dilution and start by spraying that at the top of the panel simply to reliquify the crud and let it start falling off the panel. Make...
I use a regular hardware store 1gl tank sprayer w/ wand w/ ONR to pre-wet the panels before I even hit it w/ ONR & BRS for rinseless. It gets most of the crud off (at least where I live).