The IP with chargewizard is a good choice and I think the WFCO is another with a good battery maintenance mode.
For RV's, a converter that has intelligent, 2 or 3 stage charging plus a maintenance mode that will keep a full charge and use some technique to inhibit sulfation is a good way to keep batteries healthy and long lived.
As for size, most folks don't need much more than 40 amps or so. That will charge 2 batteries at a proper clip and take care of most common loads. But, if you spend a lot of time connected to grid power and use a lot of 12v
accessories, you might want a converter with a bit more capability. Excess capability doesn't hurt.