I used to do similar and found that there are screws holding the inside door trim on at the top of each door. Put some D rings at those points and slid an old tent pole in a large U shape. A couple of nylon shower curtains was enough to protect water spray from hitting the doors or going inside.
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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer