What should you use to protect doors from getting wet?

Answer 1: Get some indoor faux leather upholstery and cut it down to the right size for average car doors. Then use this to cover the door prior to install. 

Answer 2: Carpet Shield works quite well. 

Answer 3: Use the liner from your window film, especially from big pieces of film. Then pull the sweeps and place the liner over panels prior to install. 

Answer 4: Microfiber bath towels are quite effective for protecting door panels. 

Answer 5: Use file covers that are draped over panels. 

Answer 6: You can avoid this issue entirely by trying to limit your water usage when working on these doors.