I came across these for the first time today. A polycrub is, apparently, part way between a polytunnel and a greenhouse. It is (can be) a similar size to a polytunnel and has the usual hooped frame that a polytunnel does, but has a twin-wall polycarbonate sheet skin as might be found on a greenhouse where glass was impractical. The lower parts of the side walls might be made from timber.
Given that our weather is becoming more stormy and violent they might be a solution to covered growing that is preferable to both a greenhouse and a polytunnel. It’s not like I need any more project ideas, but it might be an interesting thing to try to build on a small scale to see how it works out here in the south-west UK.