We had a 2 stroke Tohatsu 9.8 hp we purchased in Panama City after our Yamaha 15 was stolen in Shelter Bay Marina. The 9.8 weighs in the same as your 3.5 (45lbs).

We put it on the inside of the stern rail on that Edson thing you mentioned. Yes it is expensive but it was good, strong and still looked almost new after 10 years. We probably would have purchased a smaller, cheaper mount if it wasn't for the 15hp Yamaha. The Tohatsu didn't need it. The Yamaha was about 70.

Inside the rail because our method of stowing was to take the outboard off the transom and put it in the dingy, then raise the dingy on the davits and when the dingy was raised I grab the engine in the boat and put it on the rail. Really simple and easier than one of those stupid engine hoists.

45 lbs for 3.5 hp? that's a 4 stroke for you. We ran our 2 stroke on about 1/2 the gas/oil mix. The idea being it didn't smoke and would probably be stolen before it wore out prematurely.