We ended up going with a custom roof rack from DIY Van which you can purchase from eBay.
Our parts list can be found below with links for those who have 159 wheelbase Promasters!
4x PM Attachment & 9 hole bracket (sold in pairs, 8 total)
6x 3680 Internal Fasteners
6x 4295 2 hole Corner Brackets
4x End Caps for 8020 bars
3x 57" 1502-L, Black (cross bars)