I had pretty much every style of mounting a trolling motor on my 20xd, I think I like straight down the middle the best. But TN style is what I have now. It adds a bit of weight to passenger side.
the 20xd needs to been driven more then a 21xd in rough water. But even canadabullet will admit my 20xd rides smoother then his 21xd.
For rough water a hydrofoil and a negative trim wedge is mandatory on a 20xd. Was actually in 3-4 footers yesterday with my boat. We stayed dry :)