I take my Zodiac to Lewis every summer so know exactly what you mean about not seeing other boats. During the summer - visitor numbers do increase, however I've been fishing with my brother when the weather isn't necessarily suitable for pleasure boating, and on these occasions we haven't seen a soul or another boat all day.
Although the Zodiac isn't designed for an auxilliary, I decided to fit something as I'd seen another Pro 7-Man with exactly the same engine set-up (the boat with the Tohatsu 40hp Autolube pictured provided the inspiration.) Although I service my engines myself and I'm meticulous in their care, there's always the unexpected. Like the time I was out and missed a submerged log (probably 12 -15 feet long), that probably originated in Canada, or the numerous fishboxes that float just under the surface of the water, floating rope and general flotsam, the list goes on.
I have to admit that having an auxilliary can be a pain, but it's essential, especially on the west coast. I fitted a stainless-steel Plastimo adjustable bracket and cut down the nylon transom bracket so the main Yamaha engine can turn full lock. I also sourced a new Tohatsu 2-stroke 3.5hp long-shaft engine. When underway, the engine is in the raised position and tensioned with a ratchet strap to a stainless steel U bolt on the bench seat. As a precaution, I've added a hardwood peg under the engine bracket to support the outboard leg. Tohatsu's alloy tilt/support push-bolt simply isn't up to the job, especially in rough seas, where it would break. The engine only weighs 17kg, so doesn't effect the handling of the boat. It has an integral fuel supply, but I usually carry 50 litres of fuel in separate 25 litre tanks and an emergency 5 litre tank. I also fitted an inline fuel filter to the main engine as a precaution.