Regarding a vent holes. I wrote to Elektron tech support official and they replied that it is better to have a vent holes for my AR. Not a requirement, rather a recommendation... Why wouldn't people selling those ears on Ebay make such vent holes?
I am building something like this with the vent holes for my AR:
It will be 20mm acrylic, on the bottom I am planning to make a rubber feet to prevent slipping on the surface