I've been to many shooting ranges, including my own low-budget, low-tech range at home. You had said that your bench would be covered or enclosed...I think that that's a great idea. At all of the covered ranges that I have gone to, the benches, whether concrete blocks, poured concrete, or wooden benches, have most everything covered with either Graybeard's marine carpet, or old left-over carpet. Since it will be covered, the carpet shouldn't get too wet, but I agree with Graybeard...the marine carpet should probably be the best option.
My bench is made out of 2x4 and 2x6 pressure treated lumber, left over from a building project. I found some plans for the bench in an old "Progressive Farmer" book, but the magazine has probably been thrown out by the wife several years ago.
In addition to your stated target distances, I would add a 50 yard target. I find that many of my shots on game are at or around 50 yards, and I like to practice at that distance as well.
If noise is a problem, I've also seen pieces of used carpet (let's say 48" wide by 24" high) hanging from the range roof. These carpet pieces are hung horizontally 5 or 6 deep and placed a foot or so in front of the shooter and maybe 2 feet above him. When one shoots from the bench, the carpet gets blown forward and I imagine, collects much of the muzzle blast. The roof can also be constructed to slope slightly downward and past the shooter to harness more of the muzzle blast and noise. I've seen this style of shooting bench in some of the more populated areas.
Happy constructing!