There are two parts to finishing the interior of the Flare: 1 trim ring 2 foam and fabric to finish the interior of the flare. If you have a 144 Sprinter with Flares, we have a turn key product for finishing the interior. Click HERE to be taken to the 144 Trim Ring Product Page. Click here to be taken to the Interior Finish Kit page.  For all other vans, we are constantly updating our product line and may have trim rings now for your vehicle. Check the shop by vehicle page.  Here is what most conversion companies do: Build the "ring" or window sill and header, the part that connects the flare to the finished wall of your van. This is best done by using bendable plywood also known as flexiboard. Cut 6" wide strips, 48" long and staple two together to build a ring that will sit inside the OEM window cut out. From here, scribe the wood to follow the tapered contour of the flare, sand it down and wrap it in the same foam and fabric as the flare. Use silicone to attach two wood blocks between the OEM opening and the flare which will give you two attachment points to screw the ring to. Here is are professional flare interior install videos by Freedom Vango. Professional installation by Outside Van. Sprinter 144" Trim Ring