Well I can confirm a 9" sonar (Garmin EchoMAP Plus 95sv) is sweet on the boat and on the ice as well.
I built my own ice pack with additional Garmin components so nothing needs to be removed from the boat other than simply detaching the head unit ...
- Bail Mount with Quick-release Cradle (12-pin) (echoMAP™ PLUS 92sv/93sv/94sv/95sv) (P/N: 010-12673-03)
- Threaded Power/Data Cable 4-pin (echoMAP™ CHIRP) (P/N: 010-12445-00)
- GT10HN-IF Transducer (P/N: 010-12677-00)
- 8-pin Transducer to 12-pin Sounder Adapter Cable with XID (P/N: 010-12122-10)
... plus a soft case, Lithium-Ion jump starter and related home-made power cable/termination.
And yes, it's a bit pricey whatever route you go.
By the way, the additional features provided on the Garmin 7" and 9" Garmin EchoMAP Plus models (touch-screen, memory buttons, shortcut keys) are AWESOME!