I am getting ready to put togeather the pick-up box for a Dodge little red express. Rear fender surface where it attaches is flat. The pick-up bed side is also flat except where there are impression. What did they use or what is good to use to fill those gaps to keep mud and water from flying out from the rear wheels onto the side of the bed?

Thanks,
Jeff

Have a Dodge dealer look in a parts book and see if there were filler seals in the reinforcement channels. If so at least you can get an idea of what they look like. I thought my '62 D100 utiline had small rubber seals but that's been so many years ago I can't swear to it.