My name's Kel.
The simplest approach would be to make a lid to fit over the metal enclosure.
Use 3/4" thick pressure treated plywood.
Cut it so it extends 2" beyond the perimeter of the metal.
Attach a piece of 1x4 so that it runs along the edge where the lid will butt up against the siding. This piece will lay on top of the metal causing the lid to be pitched for drainage. Attach a piece of vinyl weather along the edge that butts up against the house. The weight and friction should hold the lid tight enough to the house to prevent leakage.
Attach pressure treated 2x4 to the under side of the lid that's just slightly smaller the the metal. The 2x4 is positioned to follow the shape. This positions the lid over the pit.
Attach a flexible weather stripping next to the 1x4 toward the outside so that the weather stripping rests on top of the metal edge when the lid is in place.
You may need to use either caulk or mortar to seal any gaps between the metal and the foundation. Mortar for large gaps -- say 3/4" or greater. Caulk for less.
If this is beyond your skills you could hire a handy person.
I'm not recommending the clear plastic covers that fit over these type metal enclosures. They won't seal at the house and critters can get between the cover and enclosures.
Have I answered your question?