Yes and yes yeah I've been out in some good conditions to test the setup they socket is screwed to the seat retaining strap bracket in the centre just behind the seat in my PA14 so it doesn't get waves breaking over it like the front but if im getting the swell from behind which i often do then i guess it gets splashed, as for still using it as stayed im suprised it hasn't failed and it's in remarkable condition I've now setup my shark shield to run out of it for when i need that for offshore use, i do give them a spay now and then with the hose and then other times with inox the socket has a rubber cover for when not in use. I had been looking at some type of onboard power supply and looked at many types of outlets and fitted the cigarette socket as intrim fix but as time went on it proved to be lasting, i would like to fit another in the cockpit for charging lighs and phones...... but up till now im just using a 8Ah portable power pack, it works but the usb outputs have played up before
Imo it's the stuff inside the hull that gets the worst punishment, as the inside of the hull get saltwater inside and it often just collects in places, drys then when its warm and you get humidity and any other moisture in there is just corrosion heaven, although i spray the inside of my yak out quite often and then always leave all hatches open when put away it still smells hmm fishy yes/no just smells lol and I've never had fish or bait inside the hull.
I've had wiring issues when i had the SLA in a sealed box under my seat but in the hull but i think these may have been caused by the battery leaking as one of the terminals corroded and i think this was an acid issue not salt. I gave great thought about changing to li ion batteries from SLA and once i bought the bigger sounder it really became my only option however in hindsight i would have done it way earlier if i had looked at all the advantages
but the 17.5Ah is not cheap and i think the smaller one in a waste of time tbh i would definitely recommend the FPV 17.5 or any other brand thats as good or better and to use a hobby charger (so you can tell how your battery is and how your using it) if your serious about kayak fishing.
One of the problems I've found with diy ideas from others in this area is you never hear whether they've failed or not, and of course tech changes before you buy it so there's always somthing better lol