Don;
I'm currently rigging my Trident. I placed my FF on a miniram mount on the right side of the sonar shield. I highly advise you NOT to use the sonar shield with the humminbird products. They are waterproof - yes. They float - yes. They are ipx7 - NO. They are not submersible.
By placing your Hbird above the deck, you will get many many years of troublefree service. Remove the head unit before launching and landing and store in a dry bag.
The problem lies more in the mount than the head unit. Having your mount permanently mounted below the deck is a bad idea... OK has a lot of bad ideas on a great hull. The corrision from the connectors on the mount will evetually affect your head unit and then you are screwed. I can only guess that the design engineer fishes fresh water, that's why they think they can actually store rods in the ROD POD. You can't fit saltwater rods in the damn thing.... don't get me started
I looked at other FF, but they suck. They picture just sucks for anything under $300. Hbird rocks and I'm sticking with them even though others have bailed.
I just buried my 300TX. It lasted a long long time. Hbird no longer replaces the 300tx head unit. So I upgraded yesterday. I got the 727 from West Marine. It was $50 more than the 717, but it's being taken out of the WM product list. I also order the quad thru hull xducer and will send the other back for a $59 refund.
I hope this helps. You can get the mini RAM mounts at AYS or online.
BTW: unscrew that stupid ass sonar shield and was the BOWL for other things like dikes, hooks, squid, cat food, trash, remote control or it makes a great pisser...
BTWW, that stupid cup holder works a lot better if reverse the hatch cover so your beer isn't resting on your nuts!!!
AC