Umm, I have an M.Toulouse and I couldn't be happier! What do you mean by V shaped vrs U shaped? *sctaches head*
My suggestion is to get a Professional Saddle Maker/Fitter to help you out. My TB changes shape all the time as well, as well as being very difficult to fit and A symetrical - I go with a wider saddle, and pad up.
He is narrow in the withers, but has broad shoulders and a broad back, so I cannot get a saddle to accomodate his withers, because I'll no longer be accomodating his back and shoulders and I'd be hindering his mobility and movement. So I have to go wider to accomodate his broadness below, and pad up to accomodate his withers.
Right now, he has muscle atrophy behind his shoulders and eventually I'll beable to take away the shims, once those fill out, and his topline is in the process of developing and becoming stronger, eventually I'll beable to take away the 1/2 pad, but for now, it's serving its purpose.
I love my saddle! Puts me in a perfect position the moment I sit in it, I am instantly balanced over my feet and I feel solidified in my tack. To boot, it fits my horse beautifully.
I personally do not like adjustable tree's. Their advertisements are about being able to fit a wide variety of horses, which is a load of phtphthp as far as I am concerned. You cannot change the shape of the tree, the angles of the panels, the gullet channel width - all you are doing is changing the width of the tree from narrow to medium and etc, etc.
My suggestion is to go the route I am. A wider tree that will accomodate your horses shape when they are developed and full, and pad up for now until you reach that point. Overtime, you can remove the shims and remove the half pad all together, until that point, you are protecting the back and allowing it to develop.
I'd still contact a saddler. You can contact Lynnda at Classic Saddlery. She is very helpful and knowledgeable. www.classicsaddlery.com
and will help you via phone and e-mail.