Trying to find a reasonably priced, waterproof, man-portable, lockable, storage box that can shrug off sitting and standing on it.

In the size range of minimum: 40" long, 15" wide, and 12" deep; and maximum 48" long, 20" wide, and 18" deep. Big enough to hold a long gun or two, for example. Small enough that at least a couple fit somewhere inside most vehicles. As light in weight as is consistent with other parameters.