I had an aux on an older 20 footer, it was on a drop down spring action bracket system and held my 6hp merc I had at the time, so you could keep out of water or drop to how deep you needed. Sure they are still sold, but would depend on how you have the choice to connect to your transom. Similar to this but was think mine was more robust and quality
https://www.ebay.com/itm/OUTBOARD-AU...-/232214411832
It did work the 2 times I used it and never cavitated, but a 77 model 200hp Johnno, I had a reason for it. Never do it again with a new 4 stroke well serviced.
The third time I shoulda used it coming home from Broughton Island and ran out of fuel 5 k's off home. I didn't, and stupidly threw my 12 litre fuel for the aux motor into my main tank and made it another 2 k's and the got a tow home, DOH. Lesson learn't could have gone 15 k's on aux at 3-4 knots , made it 2 k's on a thirsty 200 sloshing 12 litres around.
Cheers
Muz