Help with choosing proper converter amperage

If you could make a diagram of how the converter is wired to the batteries in your RV, that might be helpful. If you were satisfied with the charging performance of your old converter (that is, you didn't have to spend long hours with the generator to charge the batteries on a regular basis), then 60A should be perfectly sufficient going forward.

It's hard to make specific recommendations without more information about your use, your batteries, how your particular RV is wired up (wire gauges, lengths, fuse or circuit breaker locations and values....), your generator (if any), and so forth.