Neal: Since I used 3/4 inch boards, I bought the thickest 1/2 inch screws I could find that fit the 6 inch brackets. The smaller brackets (4 inch) come in their own plastic bag and have the proper screws to fit.
Mine is 35 feet on either side, plus another 15 feet across, making it 100 feet of track, times two. That's a lot of board weight to support, and that's why I doweled everything. If you pull down on it, it will bend. That's a good thing. I also have four engines and nearly 100 cars up there. They really don't weigh that much, and the boards never bend with their passing. If I ever find a weakness, I can pull down the backdrop and add another bracket. I hung the backdrop with velcro for two reasons: First, you can't nail it, and glue is out of the question because it would ruin the surface of the beam boxes. Second, in case I need to add a bracket, it's easy to get access to the wood.
I thought about adding molding for the outer edge. The inner can't be seen due to the height of the shelves and the backdrop. I decided against it. First, it would be VERY tough to bend it through the corners. Second, any molding would have as many seams as it would cover. I like the look of the natural wood, and the shelves were stained and sealed to match the boxed beams they're attached to. Finally, when the painting is done, shoot the artist. Constant tinkering with the shelves would probably ruin them, in my case.
Good luck and keep us posted.
Jerry
