Securing batteries

[rigspelt]

You wouldn't think a person handy with tools would have to ask about this, but I haven't come up with a tidy solution. Our two batteries sit one above the other on shelves facing into the galley beside the port side of the engine front. Very easy to access for maintenance. They each sit in a plastic battery box, held down with a single web strap. The straps need replacing. The only ones I can find have those fiddly plastic loop mechanisms that never seem to draw down tight. Any suggestions? I don't want to build permanent boxes because then it will be hard to get at the batteries. A better tie down product would be ideal, I think.