Well you shouldn't need a trickle charger at a voltage loss of 10% per year. Think of it like a cell phone or laptop. They may be lithium batteries and aren't supposed to have a memory but if you keep it connected to the wall all the time, it won't last very long when you do take it off. That's a guess but it makes sense...
Also damage typically occurs when the cells drop below 2v each so 8v total. Your bilge will barely run at 10v so unless you leave something on overnight, you'll be fine. Cycle time is supposed to be between 1000-3000 cycles. I know I've owned my Deka for about 2-3 years and I haven't come close to charging it even 1000 times.
One more consideration that I've found wierd. The site says to use a normal charger but many normal chargers are designed to stop charging at roughly 12.5v-12.75v and aren't true peak chargers that can detect voltage drop once fully charged. These batteries are fully charged at 13.6v and not ~12.6v. That's roughly a 8% drop in useable capacity or an actual A/H rating of 4.2 a/h for the 8 cell battery and a 6.3 a/h for the 12 cell battery.
