I have never known them to not come with the brackets in the max-air brand, but I am sure these brackets were the same brackets that have come with the dozen or so max air covers I have bought over the years, they wouldn’t be common to anything else with the elongated holes for the carriage bolts and stiffener stamping in the L part of the bracket… I can’t speak to any other brand though…
I have seen some max-air in the clearance section missing the brackets (most likely a returned item)… I don’t think you can buy just the brackets…
It would only be a guess but with a predrilled hole in the bracket sized and that aligns with the existing vent screws I can see this happening… what I can’t see is someone drilling new holes anywhere without reading the installation instructions first…
EDIT: By gosh they do have the mounting kit available..
Always included with the MaxxAir Vent covers, now offered as a stand-alone product. Mounts to the vent side wall to avoid drilling holes in your roof. Stainless steel and aluminum. Not to be used on Fan/Mate® or Turbo/Maxx® models.
http://www.adventurerv.net/zero-leak-maxxair-maxx-air-vent-cover-mounting-mount-kit-camp-pi-1020.html
sorry...