I’ve had good experiences with a product from Lowes ( usually in stock ) called:
Royal Mouldings Limited (Actual: 0.375-in x 48-in x 8-ft) Common Board PVC Board
Item # 677203 Model # 0287808021
Cutting it down has been the most difficult part of it. Use blades with fine teeth. Course toothed cutting tools will leave a rough cut and blow PVC pieces everywhere ( not that I would know ).