That is what I was going to warn people about. Whatever you use secure it in the box. Don't need any projectiles taking out our friends and families.
We actually had a 5/8 sheet of plate steel bolted to the floor of a 3/4ton work van. Went in pretty easy. Getting it back out when my boss sold the van was interesting. Had pretty good traction thoughI lifted a customers truck on the hoist,seemed awful heavy. Didnt understand until i set it down and took a close look. 4x8x5/8" steel plate. Now in the event of a collision,who knows how far it would go and what it would go through. Scary if you ask me.
Someone told me about a truck that had a 2" thick plate between frame rails and was bolted in. Took almost a day and a forklift to remove it. Guess previous owner wanted traction in a big way.
Buddy bent his box/cab when he decided to give another truck a tug,booted it quad rolled back and when he came to end of strap the quad slammed front of box anbenit,rear of cab and window even curved ever so slightly. Told him to strap it.I like a snowmobile or a Atv they won't fit through the back window when you hit the rhubarb, just be sure whatever you put back there for weight tie it down.