Unsure of the width you require but have you considered Copper Roofing tile "straps" - I bought a pack for only a few pounds, perfect for mechanical squonk boxes to replace steel parts. They even come with a 510 suitable hole at one end so both parts of a mech mod box can be replaced/upgraded being long enough to make both parts for dual or single battery.
They are not coated & you can get shrink tubing to cover exposed areas.
A hammer and nail (+ a light tap) will add the raised [nipple] section required for a safe battery contact.
If the images display below, this is what they look like.
Found in diy section(s) of ebay & amazon.