Storage box

I was wondering if anyone makes a storage box like ISOTA, but thats not 600. I can’t justify that kind of money just for a box.

I currently have a Super ATV one, but its not large enough to fit some of the things I want in it. There is enough room in the bed, the box just dosent make use of all of it.

What I am trying to fit inside is a tent and some other camping items. I want to go on some overnights and the Super ATV one just isn’t large enough. If anyone has any ideas I would appricate it.