I bought one of those plastic battery cases for the new 35A controller for my MiniST2, but using it wouldn't allow enough room to also use the U-lock I have to protect the battery from blank-key theft. So I went without the case and just silicone-RTV'd the seams as cheap insurance even though it has a gasket. That's the white schmutz you see in the photos below - once it fully cured I used a solder-flux brush to break off and whisk that junk off so it looks better now.
As for mounting, it's strapped to the tube with heavy-duty UV-resistant zipties (
https://amzn.to/3bU01ET), with this heavy-duty velcro in between the tube and controller to keep it from shifting and damp a bit of vibration:
https://amzn.to/3pmG6RPIf somehow both zipties broke, I'm confident the HD velcro alone would hold it in place, even though the contact patch against the tube is 1/2" wide at most - that stuff is STRONG, as is the adhesive backing on both sides.
And thumbs-up for Paul's referral above to CC's video - highly recommend his site; his vids are fun and useful to watch even if not directly applicable to you. His latest Rover mutation is a fire-breathing monster of a bike now.