I have a couple of them. They are light weight, which is why I like them, but they won't hold up to use with progressives like previously mentioned. I use mine for shotgun loading with a MEC 600 Jr and an extra top for a lubrisizer, and still an extra top that I bolted a 24x24 piece of plywood onto for use as a table at the range.
I don't think you can fill the base with anything. If I remember, it's hollow, but not enclosed.