What size solar charger to maintain batteries

Depends somewhat on the type of coach you have. I have 260 watts on top of mine and when I turn everything off including inverters that works for our coach. We have an all electric coach. If you forget and leave the two inverters on it will drain the batteries.

You did not post your coach. Basically you need to figure out what draw you have and then put up something a bit more. Our coach has all kinds of stuff that just won't turn off. Smaller more basic coaches do not.