My son has XLI too. When he was a new born, we covered his whole body. Looking back, I'm not sure if that was necassary. Just be careful of overheating with the summer months coming. I used to give him a cool bath, take him out and "lube" him up. Then stick him back in the cool bath because he was so hot. We also let him splash his feet in a cool sink, and got a kiddie pool (as he got older) for him to play in. Our car didn't have A/C (I know, unheard of!) and I would bring a wet towel to put on him.
Over the past 6 years (he's 9 now) his aquaphor needs have reduced. Now he just applies to hands, feet, knees (back of especially) and face. He actually develops a rash on his stomach and back if we lube him there.
If you don't see a need to apply it to his trunk, then give it a try. If it becomes dry and looks uncomfortable, just stick him back in the bath and reapply. [img]http://www.ichthyosis.com/ubb/smile.gif