Vinyl Storage Options

@dmk_calgary You have 3" thick slabs of red oak? 15" supports is complete overkill. Have a look at the sag calculator. Hardwood has much higher stiffness compared pine/MDF, so longer spans can be used. 

I used 1" red oak and 3' = 36" spans are perfectly fine. I also prefer rabbets/glue/dowels over screws. Much stronger connection.

Have 6 walnut Sefour RS 300 units that store between 75-100 per cube(90 avg.) with 4 cubes per unit. Initially purchased 2 units to determine quality, realized I hade found a "diamond in the rough" and quickly ordered 4 more units(should have ordered 6). Unfortunately the order was backordered for 21 months! Currently these units are not being manufactured but on the bright side Ocean Beach Pallet Co. appears to have high quality/aesthetics and fair pricing. OBPC is at the top of my list when ready to purchase after some needed minor vinyl purging this summer/fall.

@oberoniaomnia - you may want to re-read and actually comprehend my response.

I have 2 of these, and another bookcase, that is becoming a record cabinet. 

https://scandinaviandesigns.com/products/hendrick-media-cabinet

Music Box Designs, built like a rock and attractive, several colors of wood. Great customer service. Worth the shipping from Netherlands.