Super simple but strong wall brackets for ~1" dowels you can buy at Home Depot or similar. I built this to hold 16-17 spools with 48" dowels. Mine measured 1.02" (25.9mm) in diameter so that's what the holes are in this design.
Quick and dirty FEA is of 150N loads at the holes (easily safety factor of 2+) for PA. Basically you shouldn't have an issue for this amount of load. Make sure you have solid wall fasteners or you've hit studs!
Printed at 3 wall loops, 15% infill. 2hrs 50 mins on X1C.