Same with mine. With some wiggling I got mine to snap it, and it's solid, which I like, I often have scuba tanks in the back. It is nice that it fits really solid but you can move it without tools, even if it is a bit tricky to get it to snap in place. I don't expect to move mine that often, so...
go to harbor freight and hit every aisle and spend $100.
I have some soft nylon tool bags from Harbor Freight. Yeah, you can spend more and buy better stuff than what harbor freight has, but my good tools tend to stay home and the tools and gear I keep in the truck tends to get lost, beat up...