There may be different versions of that lid, on mine it just snapped off with a bit of prying.
PS: My IOTA ITS-50R went in the trash several years back when that model was found to be the source of several RV fires. A couple of the RV manufacturers recalled their IOTA ITS-50R ATS and replaced them with a different brand. Iota claimed all the overheating and fires were due to loose lugs, but independent investigators found components and wring in that model undersized for the max loads, especially when the AC were running in high ambient temps.
http://www-odi.nhtsa.dot.gov/recalls/recallresults.cfm?start=1&SearchType=QuickSearch&rcl_ID=11V577000
