The regular brackets mine came with are perfectly fine for mounting to the OEM rails. You don't need to buy anything extra if you don't want to. $80 for a couple of stamped brackets is a ridiculous waste of money BTW.
If the brackets the awning you purchase require a horizontal mount you can buy 2 of these for about $10:
(FM-015-A) 15 Series 1.5″ Floor Mount Base Angle | TNUTZ