what do you use to invert your baked half sheet cakes to cool ? I don't like to use cooling racks since they make marks on the cake. I know I can use cake boards but I want to use something sturdier than cake boards.

I use a cookie sheet that does not have rims. Or if it is being transported in the carrier...then I put it right on the carrier's bottom piece.

i use cookie sheets and also i have a really thick big wood cutting board that is heavy but absolutely the perfect size to flip a full sheet cake. HTH

For the 12x18 pan, I use a 16x24 cooling rack. Lay the rack on top of the cake, hold hte rack in place and flip the rack/pan together. Place a 2nd rack on the cake and flip it back so the cake is now sitting on it's bottom. Shouldn't be any problem with lines this way.

Lines get covered up by icing, so I'm not sure why that's an issue.