I had a wheel well that was dented in on my 92 civic 4dr so i filled it with fiberglass it looks ok but their are small holes in it how do i get rid of these wet sanding? also i have some miner rust under the wheel wells and on the little lip if the wheel well next to where the bumper attaches would spray undercoating work on this to help stop it? i heard their is anti rust gel that stops rust also anyone have any ideas