<pedant>
Were "stupidist" to enter the lexicon, it would likely be defined as "one who practices stupidity." Ref. pugilist, columnist, exorcist, etc.
As an alternative to "most stupid", "stupidest" follows the form of other superlatives. Ref. tallest, smartest, prettiest, etc.
"Most stupidest" would be a redundancy and grammatically incorrect, similar to most tallest, most strongest, or most loudest.
</pedant>
<opinionated w4nker>
Personally I don't like the side mount for cans, although they do double as security for the windows.
</opinionated w4nker>
<helpful forum guy>
The tracks the can frames mount to look like Mac's VersaTie track, sold in the UK by Mudstuff. This you may all ready know, since the picture you posted is on the Mudstuff cargo control page. Mudstuff doesn't list the gerry can holder, neither does the Mac's home website. Perhaps a call or email to Mudstuff to ask about the photo?