100-150lbs of jacks up high on the vehicle doesn't sound appealing to me once you factor in the weight of jacks. Since this is for a ute bed, you'd be better off working to put them between the frame rails under the bed. There is a 4" or so tall gap between the bottom of the bed and the normal ute cross members, the only tricky part is the member across the rear of the ute bed comes down a couple inches so it doesn't provide straight on access, however a modified rear member could solve that one (or they might be able to slip up in there as is). You'd need to make up a compartment to hold them securely and shield them.
You can sorta see what I mean in these shots. The entire area between those channels is open except when you get to the back of the bed you can see how the rear member covers about half.
