Making a bezel from scratch will be more involved, but if it yields the best results, that is probably the route you should go. I faced a similar situation and chose to simply mod the existing dash bezel because it had a number of compound curves that I felt would be difficult to match and locate proper mounting points.
When I modded the dash, I used a combination of plastic, as I had some pretty big fab holes to deal with and bumper plastic. The bumper repair plastic is basically epoxy, so lay it down and smooth it out as close as you can, then use a file and various coarse to medium sandpapers to get it close, let it dry, then fill the inevitable spots with more bumper plastic and repeat.
To get it silky smooth, after sanding the bumper plastic as smooth as I could, I used glazing compound, which is much softer and requires much finer grades of sandpaper, eventually getting it down to wet sand and 800 grit.
Then I sprayed the whole thing with texture spray paint. You can also use truck bed liner spray on. Both worked pretty well and turned out decent. I'm no pro, so there's always room for improvement, but the results were better than I expected them to be.
Details and pictures in my worklog.