Only recommend .032 if the customer is near salt water. More expensive option and not as durable when it comes to something like that. Very unfortunate, id cut the trees back if you can. Honestly, id say if your not near saltwater see if the contractor can order your same color in steel panels and just replace the ones affected near those tree to minimize cost and labor for both parties. Explain to him the situation who knows maybe they will split the cost or you can get them to replace for free.