I'm looking to upgrade from my junky fish finder to one of the smaller GPS/fish finder combos. I have a hard top on my 23 WA, and I'm wondering if a unit with the internal GPS receiver/antenna will work ok under the top. My hand held GPS unit works fine underneath, but a guy at Bass Pro Shops told me I would need the external connections. If it helps, I'm looking at the Hummingbird 383c and Lowrance M68CS units right now.