Better to charge and store for a period.
Leaving on trickle charge will eventually result in the internal water being boiled off with time if the terminal voltage goes much above 13.8v. Best is to charge periodically, if you want to use the trickle charger use a time switch to only provide a small topping charge once a day for around 15 minutes, which will compensate for the loss during the standing time. It will provide enough to keep it alive, but without overcharging. Check every month though, so that you can see if they are losing capacity ( record cell voltage after it has been resting for around 30 minutes after charging, which will give you a trend as to state of charge) or staying fully charged.
