My thoughts on the matter, and admittedly I have no experience with a 222 Fisherman, but I'd either mount something inside of the electronics compartment/dashboard behind the wheel or something outside of it. I've got a 2004 GW 228 Seafarer with a Garmin 943xsv located inside the electronics compartment and really like it there. It's protected from the elements like the sun and the rain, it can be locked up, it's easily visible when either standing or sitting and I have no complaints with the location. I prefer Garmin over the other brands for being easy to use and from what I've seen, really good products that seem to be at least comparable to the others out there. I also prefer touchscreen only, and without any buttons on the MFD, so that's one of the reasons why I went with the 943xsv. Another reason was the price in that I got it for $1,399 and didn't want to spend another $1,000-$1,500+ getting a larger 10"-12" unit. A lot of guys have pulled off the screws/hinges and enclosed the compartment with starboard or something similar and then flush mounted a display on the outside. I briefly considered doing that and then decided to go against it for the reasons stated above as well as I didn't have the time or resources available right before replacing my old unit.
The old unit was a 7" touchscreen Garmin from around 2010-2013 that went belly up on me when I did a software update, and of course this happened like a week or less from the king salmon opener. The previous unit was installed in the electronics compartment, so I just continued to use that area as well for the new one. As mentioned before, lots of guys have done the flush mount thing and have been happy with that. I don't like it that way because it's not secured, it's exposed to the sun all the time as well as any inclement weather like rain, etc. If you're looking for a 10"-12"+ unit that is touchscreen and is from Garmin, I'd consider the 8610xsv, or the 1243xsv. If you don't like touchscreen and want buttons on the MFD, there's the Garmin 1242xsv as well as the Echomap 106sv as well. Lastly, I don't think mounting it in the electronics compartment above you would be very comfortable in that you'd be staring up the entire time, especially when sitting down. Obviously the 228 Seafarer and the 222 Fisherman are quite different in terms of boats and layout, but it seems like the overhead electronics compartment is almost straight up, and that doesn't seem comfortable looking straight up, especially when sitting down. Here's a similar boat to yours for sale on BT, I don't have any affiliation with it, but it shows a few pictures with potentially some different ideas as to what you could do with your setup. And I'm sure someone will also be along here shortly with some firsthand experience as well, but either way good luck and welcome to the forum.