Hi Westcoaster,
Also a member of the ‘I have an auxiliary’ camp. Only a tiddler 3.5 but easily pushes us along at max hull length displacement speed of 5 knots at half revs - more revs, more noise, and no quicker.
We simply clamp onto transom, attach a rope safety leash and usually ratchet strap down. Sometimes store inboard, for long fast lumpy trips, on a bracket fixed to transom knee - sorry no pics.
Although full steering available with aux, found much more control steering with main. Perhaps a tad more drag but certainly less frantic.
Also concerned about protecting transom gel/flow coat. For a protector we cobble a cheapo liner utilising Ikea chopping mats (£1 a pair) which make four liners. Mats only around 1mm thick as we have a meaty transom only just less than outboards clamp capacity. They last around half a dozen runs, then replace.