Mounted mine in the topper on top of the on-board-air plywood cover. Used a random bracket (some sort of old truck bed toolbox mount I think?) With a bolt through it. The jack base slides over the bolt on the back which keeps it from moving any direction.
Front side has a carriage bolt mounted through the top board. It has a rubber bushing (from an old sway bar end link) to keep the jack from vibrating/making noise. Used a big Yakima wing nut to hold the jack handle down. This keeps it from sliding off the bolt in the back too.
Very cheap, and it works perfectly for me. Out of the way, stored inside, and easily accessible.
Cheers and safe hi-lifting.