[oil pan 4]

If you have any doubt you didnt get a full charge it might be a good idea to run the alternator for part of the drive if you can.
An ampmeter could tell if the battery is drawing alternator power for charging. You could use an amp meter to see if the battery got charged at night. You could give the battery some alternator power and if it soaks up every amp the alt puts out then you know it didn't get charged the night before.
At that point about all you can do is run the alternator and lose some fuel milage or get a bigger charger.

How much did that battery cost?

I am thinking that little deep cycle battery could hold around a half kilo watt hour of use able capacity so its going to want quite a bit of power.
The battery may not be able to get a full charge off a normal 14.4 to 14.5 volt starting battery charging electrical system. I have never thought about charging hard cycled deep cycle battery on a normal car system.

I don't consider my 44lb starting batteries full until they are at 15.1 or 15.2 volts and drawing less than 2 amps. A smaller deep cycle like that should be full around 15.2 volts drawing under an amp.