Here is a full sized Rebel Fleet Trooper Helmet. 12 parts including a chin cup and strap holders for the chin cup. There are 5mm holes for locating the front shield, rear swoop and comlink box for accurate placement. You can use pop rivets to attach them or small wooden dowels. Each assembly also has 2mm locating holes where you can insert toothpicks or brass wire to ensure a precise fit.
Mandalorian New Republic Shield also included.
The movie helmet was actually printed a very light grey which appeared white on screen. Paint the upper part of the front shield gloss black or dark grey. Cut out foam for the interior or glue in a harness from an old hard hat. Use two part epoxy for gluing in the strap holders and the hard hat harness.
Insert and glue a 180mm long carbon fiber rod (0.05" diameter) into the hole on top of the com-link. (Carbon fiber is strong and won't break easily or become distorted when bent).
The helmet sections are cut to fit a 12" FDM print surface. I can cut the sections smaller if there is enough demand.
I recommend to use 0.2 layer height and 4 wall thicknesses minimum. Infill set to 20 percent, but higher will result in a stronger build.