My LP shelves are made by Lundia (the company IKEA copied their shelf system Ivar from). I have them for 35 years now, fully loaded, one foot two inches deep, two feet 8 inches wide, and no warping whatsoever. Solid spruce, a little more than half an inch thick. No support. There are books on the selves, too, which are even heavier. If the wood is selected with some care, there should be no warping.
My girlfriend at the time alerted me to them. It can be assembled without drilling or screws (except for securing them with a wall attachment), can be taken apart and mounted differently in a room with different dimensions. When I moved the last time I took a list of all the parts I had and a sketch of the living room to the dealer, and he sat down with me and in one and a half hour we had a new design using all the parts and a minimum of extra shelves to be ordered. No idea if they have US distribution, but there should be something similar.