A friend added aluminium mesh (same as on security screens) between his chassis rails on a Jayco Penguin to carry long items such as his ladder.
I wouldn't trust an "under van tool box" to be there when I needed it!
Most toolboxes are mounted on the A frame or rear bumper but I'm not certain how that affects weight distribution.
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Warren
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I think we need more info on your thoughts, the chassis of a van extends from the back, all the way to the tow ball. What are you wanting to carry in there?, what's wrong with the vans boot?
I agree with macca we carry a basic tool kit in the pajero held in place with bunge cord for safety its much harder to access by others than on draw bar or back bumper
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