The general consensus is that you will do better with an actual battery charger, as compared to a battery charging Inverter/converter. You will want one of those for the conversion too, but for charging batteries, get a good quality charger. You really don't want to get to large a charger, and much above 30A will be more than you need for a 3-4 battery bank.
You may want to check into solar charging too. A couple of panels on the roof, or even these newer portable packs that you lay out when you get to a CG will do a nice job of getting the batteries back up to full charge. (I'm not talking about one of those little laptop size panels, which are really just for battery maintenance/trickle charge).
Depending on what you plan to do with the RV, you may find that installing a slightly larger Alternator on the Engine, which is wired up to your "house" batteries too, will charge those batteries when you are on the road....but it is not a very efficient method for charging when you are camping.
You will probably find several other threads about batteries, and they should be helpful.
Oh, on edit, and reading the original question...how long does it take to charge the battery? It will depend on the battery, and how discharged it is. It will also depend on the age and condition of the batteries, as well as the charger...so it could take a few hours, or it could take all day.
Good luck
