Welcome to iRV2.
Most of the trays I've seen for class A gassers and class Cs for that matter were custom built by the coach manufacturer, and factory installed; others home built by the owners.
Because of the many designs of engine covers through out the years and different manufacturers, they probably aren't a high volume item, so no one in the aftermarket makes them.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.