Now I know you're keeping this van for sure
In my Gen2, I did two layers of sound proofing for sound and moisture, plywood subfloor (5/8 or 3/4) ext grade primed/painted then HD bulk roll carpet. Tucked the carpet over the edges of the ply. Cheap but functional. I use tarps when needed to protect the carpet and make for easy cleanup.
Also, sponge rolled black enamel paint on the door panels for water protection and appearance after adding sound proofing inside door cavities. Nothing fancy, just functional.