I have also run into lot of problems when trying to change the background template on mannequin. I thought if I could use preset templates it might be helpful but I always seem to run into some issue with it.
Also it is really tricky to save individual layers in av paint you have to save every layer and even with Chip's template it takes practice to know where things go on 3d mannequin.
I am still struggling bit with it and Avpaint designers don't really have very many new user friendly guides or more detailed information about the program and the group they have for tips isn't open to general public and they aren't very responsive when I have asked them about group even though I got several friends to buy there program we sort of our own to figure it out.
Yet it is good way to get idea of where things to go.
I was given this tip by friend who I introduced to program to save certain tips different fabric or template layers like black backgrounds with texture layer in adobe then save it as psd and re-open it in avpainter helpful you select folder upload new texture.
This is helpful when erasing or working with different types of layers of textures but still have run into problems, it just take a lot of practice to get it right.
Often if you don't have certain background over the skin template when erasing I often would get these lines or dots I miss the dark background helps things show up better.
Just make sure you select the right areas and don't do what I did and accidentally delete the black background

Also make sure you save each layer separately in avpaint, even though when you close it will like it act like you missed something. it tends to automatically want to save files either as tga and merged.
Also recently I have run into problems with transparent images not showing up which is really major hassle after literally spending hours making something and getting stuck with non transparent tga file.