Need Garmin 178 advice

[Perdido Key]

My Hunninbird overheated and died plus my Streetpilot 2610 will not accept a bluechart card (I think) so I am looking at a Garmin 178 in black & white GPS/SONAR combo unit. Any advice would be appreciated.
Also plan to mount on a 19 Bay with canvas top, do I need internal or external antenna?
TIA

[Cincinnati]

When you say canvas top, do you mean a bimini? My Garmin 168 w/internal antenna works fine with my bimini up all day. My only complaint about my model is the small screen size. Look at the 178 screen size and think hard about if it will suit you in split-screen mode. Garmin makes great stuff.

[Putershark]

I have the 172c w/internal antenna and the Blue Chart chip for my area (nice box) and I also have mated this mount to the bottom of it which works great...

http://www.vexilar.com/products/promount.html

I mounted one quick release base on the boat and another in the console of my truck (take me about 10 seconds to remove) so I get the max use out of my GPS. The bimini has no effect on it, and with the angle of the windshiled on my Tundra, the top of the truck cab does not seem to bother it much either.

Tight Lines
Dave

[Perdido Key]

Thanks for the help. Waiting to see what the factory says about the Humminbird Legend 2000. Bought it last Dec off ebay new for $140.00 so no big loss. Per your advice will probably buy a color unit combo.