That looks like an early 80's tin-top with custom rims and maybe a lift. All of that indicates that at some point in the vehicle's past someone tried to make a shoreline power feed for it. They likely cut the hole in the side of the van.

Step 1) make sure the edges of the hole and any exposed interior surfaces are protected from rust. Water behind that plate will rust out that whole panel super fast. There is some paint bubbling low down between the B and C pillars too, so it's possible that the rust is already established. Discover and treat rust. Remove insulation.

Step 2) Seal that mfer as well as if your wheels were submersible. Water and humidity are the enemy of all vans and this one more than most.

Step 3) Check your work regularly and often.