Agreed, that's just going to give you more fits than anything. Do yourself a favor and just spend the $25-50 for a good quality bag to shoot off of. Either of these would do nicely without breaking the bank.

http://www.amazon.com/Caldwell-Tackd.../dp/B000BY9G5K

http://www.amazon.com/Caldwell-Deads.../dp/B002APAWY2

If nothing else just use a rolled up sleeping bag to shoot off of.

The whole goal of a rest or bag is to immobilize the rifle as much as possible without having it negatively affecting it's ability to recoil naturally. That whole rest you've made will slide across the bench under recoil quite easily thus affecting the natural movement of the rifle (they will essentially move as one when recoiling rather than the rest remaining stationary while the rifle moves).