I have never been but I'll warrant it isn't as bad as Dinas (Silica mines) and I can easily do that with a 12L twin set. I even took my JJ with twin 7s and a 3 up there - again no dramas. That trek would be impossible with a trolly.
Obviously it'd be impossible with a trolley but you're def in the minority if you describe the trek up to Dinas with twin 12s on your back as easy.
My Magnacart cost me £25 and lasted a year of serious abuse. I'd buy another one but i could do with something that extends to at least 4 feet so i dont have to bend when i pull it, better for the back if you can stand up straight while walking it.