On our last 2 conversions and our new project we use Upholstery on walls and dash areas..we color coordinate the fabrics to complement each other..on the walls we use quilt batting stapled to plywood backing then cover with upholstery fastened around edges after being stretched..use a trim to cover stapled edges called welting ;which is a piece of cording covered with matching fabric.You can make this or buy already made...Ceiling we do in panels:which are luan sheets covered with batting and ultra suede place batting on laun then covering and stretch over back and staple..use buttons to form pattern on ceiling.when they are pulled tight against luan they create a padded look..we cover buttons with matching fabric..just throwing out a idea for consideration..cost on last coach was probably less than $900 for all including 12 ft couch...learning as we go..Bob