The easiest way to do it is by getting some AGM batteries. Optima's are AGM batteries. Optima batteries have very high cranking amps(CCA), and are very resistant to vibration, and pretty tolerant of abuse. But for their size they do not have much capacity(AH) amp hours. An AGM battery that is rectangular will yield just as much ( if not more)cranking amps but have 25 to 35% more capacity. All AGM batteries will have a higher cranking amp rating than any flooded battery of the same size. Generally flooded batteries will have about 5% more capacity than the AGM battery of the same size
Battery abuse is when you discharge them below 50% and do not recharge them fully or promptly. True deep cycle batteries are most tolerant of this abuse. The next most tolerant batteries are the dual purpose batteries. These will say marine/ trolling/ RV/ deep cycle on them. The least tolerant of abuse are starting batteries. These should not be discharged below 80% and will not last long if cycled deeply.
In you application I would recommend Odyssey batteries. Die Hard PLATINUM batteries are the same thing for 25% less $.
Now to isolate them, the easiest way is with a Continuous Duty Solenoid. They look like this:
Get one rated for at least 100 amps continuous. The 2 bigger bolts are for the battery Hot/Positive wires. One side goes to the engine battery, the other side goes to the auxilary batteries. The 2 smaller wires are for activating the solenoid. When these see 12 volts from a switched source, it connects the 2 bigger wires together, paralleling the batteries. Ideally you want to the switched source to be something that is hot only when the engine is running, rather than just the key turned to on or Accessory.
You can just hook the negative wires of the batteries together.
Now it should be said that everybody overestimates The alternator's ability to fully recharge a battery. A 130 amp alternator can only output that in a laboratory, when cold, at high rpm. On top of this, the vehicles stock wiring is only adequate to power the vehicles accessories, and recharge a slightly depleted starting battery.
So There are a couple things you can do, the last of which is a bigger better alternator.
First, the wiring between the solenoid and the auxiliary batteries is very important. It has to be at least 6 awg cable for okay charging. The thicker the better.
This wiring does little good if the Stock charging circuit is not upgraded as well. The easiest way to do this is to run another (fused) cable directly from the alternator(+) post to the Solenoid. You want to wire it to The side of the solenoid which connects to the engine battery.
Upgrading the hot wires is no good unless the ground wires are upgraded as well. The negative is shared by the whole chassis. The engine has a pretty thick ground cable from the battery.
What you can do is run a fat cable from the auxuiliary batteries to the alternator's (-) stud, or one of the bolts that attaches the alternator to the engine.
Once you have done the above steps, you are at the limit of the alternator's capability. The limiting factors at this stage are the voltage regulator, and the alternator itself, and any poor connections in any part the charging circuit.
If at higher RPM and the batteries are under 80% charged, and the voltage does not rise to the mid 14's. Your voltage regulator is not allowing the alternator to work as hard as it can. If the alternator is internally regulated, nothing you can do.
There are many other ways to have batteries isolated from the engine battery yet still charge when the engine is running.
IMO, this is the easiest, most effective, automatic way.
I myself use a true manual switch.
I have my batteries under the floor behind my driver's seat and the switch in the cabinet above them. I need 12 feet of cable (one way) to reach the engine battery. I need 11 feet of cable to reach the battery switch from the alternator.
When I added another 2 AWG cable from the alternator to the battery switch and another between battery and ground, my charging amps at higher RPM's increased about 120%.
My 130 amp alternator is only capable of 32 amps at idle speed, when hot.
If you want your batteries to last( for years), you must think of the alternator as only able to supplement what your stereo use. Even with an upgraded charging circuit/ system, 2 depleted batteries are going to require many hours of driving with engine rpms above 1800 to fully charge them.
Since this is not usually feasible, you should have a good 3 stage automatic battery charger, and plug it in when you get home. Have a convenient way to do this and you can get 5 years or more out of your batteries, and never have them let you down during an outing. If you don't, your looking at about 2 years.