I realize this is an old thread but i wanted to share my recent experience using evaporust on lower dash. What worked well for was laying paper towels that were saturated with evaporust on the areas of the lower dash that i wanted to derust. Then use thin polyfilm , like 1 mil thick or so, over the saturated paper towels to prevent evaporation. Periodically remove the plastic and reapply a bit more evaporust by brush then cover with plastic. The idea is to maintain dwell time of the evaporust. The soaked paper towels conform easily to the irregular shapes. And the plastic cohesively bonds to the saturated paper towels.