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For the most part the , side rad configuration , would have to be posted by the person creating the used listing. Other than that , you, as the searcher, would have to be aware of what manufacturer, produced which models of Class A, with the side rad.
EDIT: To start your online search, chose a floor plan; by the length and layout that appeals to you; then look for a manufacturer that offers that floor plan with the side rad set up. Once you have the model number that will give you the ability to narrow your online search.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.