Problem is, an RV battery is a deep discharge battery whilst a truck batter is NOT. If you hook a deep discharge battery directly to your trucks 12v system and LEAVE it there, you can (and will) kill it by boiling the water out.
You need to go thru a devise that will limit the charge cycle...... or carefully watch the charge with a hydrometer or voltmeter and when it gets charged, disconnect it.
Old thread I know, but..
If your alternator is working correctly it essentially stops charging when a battery is fully charged.
The longest lived battery I've ever had was a Sears Diehard wet cell deep cycle installed as the only battery in one of my Land Rovers. It lasted close to 10 years.
I used of for starting and for winching.