I think that if the chord of the wing tip (including ailerons) is at least 70% of your root chord, your wing will probably not tip stall on you unless you do it on purpose with a snap roll maneuver.
In addition to wash out, you can also make the leading edge more rounded at the tips and leave it sharper at the root in order to force the stall to happen at the root first. You sometimes see this on full scale planes.