I am making 2 valve covers as a groom's cake this weekend. I chose black paper to cover the boards with. The largest boards I could find were half sheet boards, but the way I want to arrange the cakes, one wouldnt be big enough, so I bought 2. I THINK I know how I am gonna do this. I will cover both boards separately with the black and place a cake on each board kind of at an angle. Then I will lay the cake boards touching each other on the table. Each cake will also have its own board about the size of the cakes under it as well. They will be about life sized so they will each be about 5x18 inches.

Will this look ok? Having the 2 separate cake boards right next to each other?

And also, how do I keep the cake boards under the cake from slipping around on the black boards? Do I just spread a little frosting on the black cake boards so the other ones won't slip?

Having the 2 boards would work well too bc I didnt plan on taking the cakes in boxes (sinc I am laying them at an angle, I worry they wouldnt fit right in a 1/2 sheet cake box). I will just carry them separately inside.

Go get a sheet of foam core and make it real easy on yourself. Provided, that is big enough as well. Much sturdier for a cake that will have detailing and time invested.

What are valve covers?

Haha, they are part of an engine. I will edit the original post and add a picture of what they will be based off of.

They keep the oil from splashing out of the engine as the rockers move up and down. Some of them look really cool if they are chromed. (Yes, this is my 9 to 5)

Yes, definitely........foam core board.......you can get it at Michael's or Hobby Lobby or even at some WalMarts..................makes a WORLD of difference!!!!!

I agree on the foam core board. I get mine at WalMart all the time.

Thanks for the explanations. Now I have another question. What are valve covers?

I'd go with foam core board as well. If there not large enough then I would recommend getting a masonite board or sheet of plywood.
You can buy foam core board at the dollar store as well (dollar tree has them) but they only come in 3/16" thickness. If your cake is going to be super heavy or you think the board will flex double or triple it up, use a hot glue gun to attach them together.

i would put melted jam on your boards that usually works to stop slipping

I have already bought all the stuff for the cake, including the boards. I will definitely keep the foam core stuff in mind for next time though!!! These 2 cakes wont be super heavy and I have definitely carried heavier on just a cake board, so I think it will be ok this time. Most of the detailing in the ones I will be doing is just the emblem. We are doing the shape of the valve covers on the groom's Mustang GT with the "Ford Racing" emblem on the front of them.