31R
There is no insurance issue with "going along for the ride" you simply would not be insured unless you took out seperate cover.
There are many pilots out there who have done more crossings than me but I have done my fair share of piston singles and twins and small turbines. Each category has different considerations. On a piston single you would not want the weight/space penalty, probably the same on a small twin. Essentially 'thoug it is more personal than that. Ferrying is an immensly challenging but hugely rewarding type of professional flying. It takes a particular type, probably a bit insular and having another person along for the ride is just another thing (person) to worry about. That is not what you want when deciding whether to shoot for Narsarsuaq or stay put. I did loads in the 70's and 80's and after every S/E crossing (most were Gander to Shannon direct in about 13-14 hours in the days of dead reckoning only) I said "never again". 2 weeks later I was off again, I was not only missing the adrenalin caused by fear but also the incredible satisfaction of getting the job done. My last S/E crossing was 1988 until in 2009 when I had the opportunity to do "just one more". It did it because there is nothing like the feeling of touching down afer the jump. Would I do another?........ probably yes.
It is one of the purest forms of flying, it is your skill and judgement that only matters. Try and get into it if you can, you may love it, but many do not. Essential reading for any budding ferry pilot is Gann's "Fate is the Hunter". His stories are not stories they could happen to you.