The Theology of the Body has very little to do with sex and a lot to do with the value of the human being and the value of the person.
Pope John Paul II reminded us in “Love and Responsibility” that sin is “a function of the interior”, or as Jesus Christ put it in the Gospel - sin comes from within the person. This is why the Pope wrote, Sexual modesty cannot then in any simple way be associated with the use of clothing nor shamelessness with the absense of clothing and total or partial nakedness. (Love and Responnsibility).
Nudity or nakedness is not in itself sinful, immodest or indecent - this would apply to the reason for being naked/nude and would explain why it is not sinful, immodest or indecent to climb naked into the bath or shower nude. It is also possible, we should note, to express a sin of immodesty or indecency while fully clothed through one’s behaviour or words.
A tendency to over-simplify Church teaching in this area may result in the grave error of making judgements based on appearances (See John 7:24). This is something we are not supposed to do.
If nakedness/nudity is associated with sexuality, further error will result. Nudity/nakedness is descriptive of the natural state of the human being - which is of value to Jesus Christ. As such we are supposed to respect it - but do we?
This is where the Theology of the Body begins - challenging our perception of the body, how we see each other and how we respond to our neighbour.
These are just my thoughts on the matter. Nothing more.