Are there any stoic writings lecturing on dealing with insults, humiliations and even extreme physical humiliations that might drive one to commit suicide?
The following brief background to Stoic tranquillity, when renders one impervious to insults or humiliation, may be of help:
Let us see how this doctrine was worked out in terms of the traditional ethical concepts of happiness and virtue. Whereas earlier philosophers had placed happiness in the satisfaction of desires or the performance of activities, a conception which implied that men must seek to arrange the course of events so that these desires will be satisfied, which implied in short that men must seek to impose their will upon nature, the Stoics taught that the course of events is inexorably determined by Destiny and that it is sheer illusion to imagine that man can control nature or in any way alter the predetermined course of events. If happiness is not to be a mere unattainable ideal, then, concluded the Stoics, it must depend entirely on things that are within our power. In the Stoic universe, however, one thing and one thing only is within our power - our will. True happiness therefore will consist in making our will conform to the course of events, in accepting by a basic act of choice what Destiny has in store for us. If a man does that, then nothing can possibly disturb him, for he will have reached a state of inner tranquillity in which his purpose has been identified with that of Destiny. Hence the Stoic definition of happiness as the smooth flow of life.
(A. R. C. Duncan, 'The Stoic View of Life', Phoenix, Vol. 6, No. 4 (Winter, 1952), pp. 123-138: 133.)
If by virtue of my inner tranquillity nothing can distrub me, I will clearly not be disturbed by insults or humiliation.
One of the central epithets of stoicism is being one with nature. From Epictetus we understand that we have control over our minds. From this light the stoic insight is precisely the understanding that the insults, humiliations and other such things are our very own reactions on externals. The reactions from within are internals and we can control them albeit with great difficulty and practice, but the externals, do not bother. We cannot control the rain, we can control how we think about it.