Hard case that fits under rolling Tonneau cover canister

Just installed a Gatrotrax MX in my 2021 and want to find a super low profile hard case that might fit under it. Obviously needs to be width of truck bed at the cab... maybe 4 inches high. Wouldn't hold much, but it's unused space so anything might be helpful.

Starting my search... but thought i'd reach out first...

Gun cases look close, but too wide.

 

This is what I have under my hard tonneau.

 

I saw a guy put a pelican rifle case on the wheels wells and it looked really clean.

I think the picture was in "What did you do to your 3rd gen today" but I cant find it now.

He used rivenuts to hold it to the bed I thought it was real slick fit under his cover as well.