Good truck bed rails change how you haul lumber, ladders, and gear without scratching your paint. They keep cargo tied down and secure when you take sharp turns on the highway. Holiday sales are usually the softest time of year to buy these, as auto parts shops slash prices to clear inventory before the new year.
You want to negotiate the price of the rails down with the dealer or parts counter first, before you even mention how you plan to pay. A card window is just a tool for spreading out the remaining cost, not a substitute for haggling on the actual sticker price of the gear.
Remember that the 0% intro window is a strict deadline and not free money. If you still have a remaining balance on the Citi Simplicity® Credit Card when those 18 months are up, regular interest charges will kick in on what is left.