permanent bolting is obviously more secure, and if you intend to always trailer it, should be OK. Trailering on bad roads? Bolting is better. But, if you have some kind of swamping mishap, and these happen a lot with dinghies, IMO, you are in trouble. If you can't easily get that motor off the back to manhandle the whole thing, it's about 3 times as hard to manage. That would be the only downside, apart from the security aspect of being able to easily lift it off the back and lock it up in a shed. Although the bolting helps the security aspect a little.