Fergus, this is how I am doing it over the hood of my truck. First, you must have the bipod that will incline - rifle must be as level as possible.
I don't use a rear rest figuring that time is the big issue. I hold the stock in front of the action with my left hand and rest the elbow on the hood. I put a fair amount of downward pressure on the stock or it bounces like crazy. The right hand is in the thumbhole stock and pulls firmly into the shoulder.
Because the rifle also has a muzzle brake
, the recoil is quite mild. I do get to spot most of my shots from 300yds out. This is important to me as I want to know where I hit the target or animal.
I would prefer not to use a bipod at all. If you could make a big bean bag, that would be much more stable and the bouncing would be gone. There is a company making them in the shape of an X and the rifle sits in one of the X cradles. Very good idea. However, not as field portable or useful as a bipod.