We've had discussions about this topic a few times before on the board. The general consensus is that the alternator is not the best method of charging the batteries, but aside from solar, is the only method available. It's not that an alternator doesn't do a good job of charging batteries. In fact, it's about one of the simplest methods out there and works rather well. The problem comes from the fact that it is voltage sensing and will taper the charge off as the battery approaches a full charge. The end result is a deep cycle that will sit somewhere between 90-100% charged after a reasonable amount of driving time. For most purposes this is fine. It just means that you can't count on the alternator to be your only means of charging the batteries.
I would recommend getting an intelligent onboard converter/inverter/charger, a good portable automatic charger, or get a manual charger and be prepared to be a little more hands on. Schumacher makes a good automatic charger called the Speed Charge that has 2-8-12 amperage settings and a setting for AGM, Deep Cycle, and Starting battery algorithms for charging. We sell them here for $75. Your mileage may vary. Deltran also makes some of the very best automatic chargers on the market and would be worth looking in to. Basically you're just going to want a charger to bring the battery up to 100% charge, desuphate, and equalize the battery as required.
As for batteries...I would keep away from the Optimas or clones. I sell them on a daily basis and see absolutely NOTHING wrong with them...when used in the correct application. Unfortunately and RV is not the correct application. A Group 31 Optima Marine Deep Cycle (blue top) only has 75 amp hours in it. A pair of them is going to give you 150 total amp hours to a 100% depth of discharge for $450.
A GC2 6 volt golf cart battery will give you about 200 amp hours, give or take and cost $75. You will need a pair of them to get to 12 volts obviously, but you will end up a far greater capacity (meaning a shallower depth of discharge and longer living batteries) for 1/3 the price in about the same footprint.
An alternative to the wet acid golf cart batteries is a standard flat plate AGM battery. It uses the same technology as an Optima, but the plates are flat so you fit more in a given volume of battery. We currently are selling one as a middle of the road option to people with boats in a Group 27 footprint that has a capactiy of 100 amp hours (the same as a wet acid Group 27 and 33% better than a Group 31 Optima) for $170. This is CERTAINLY not the only option as far as AGM's go, but can perhaps serve as a starting point for comparison.
Basically what it boils down to is deciding your electrical load needs versus maintenance versus cost, etc. Dollar for dollar wet acid golf cart batteries are still the way to go for the vast majority of us. The closer you get to boondocking full time the more sense AGMs start to make. If you are just looking for a back up power source when shore power is not available, but plan to spend most of your time in campgrounds then the wet cells probably make the most sense.
I'm sure some others will pipe in with some advice, but in the meantime I would recommend reading Phred's Poop Sheets