80/20 Aluminum T-slot Building Systems – Build your Idea
If 80/20 is new to you, then you might also be unfamiliar with its steel channeled cousin, Unistrut. https://www.unistrut.us/Unistrut is used extensively in the US to build support structures for electrical switchgear and process equipment. You can get grades suitable for outdoor and corrosives exposure.Unistrut is the Kleenex term, there are a number of work-alike / fit-alike systems.Then for round tube, there is Kee Klamp:  https://keesystems.com/