RicMcK said:My ideas are that I could put it on the bottom of the cross tube, the bottom of the stoker top tube, or the rear rack. If I mount it upside down I will add some secondary straps to secure it. Do you think it would be OK on the bottom cross tube? I wonder if there is enough ground clearance.
Under the top tube with straps looks good. It's probably wasted space anyway, unless you normally have a frame bag there. Just check first to make sure there is no rubbing on the stoker's legs. I wouldn't put it under the bottom tube, as you probably already have clearance issues there over bumps, curbs etc due to the long wheel base and will end up scraping the battery or getting stuck on something.