To tunnel or not to tunnel

I have a 33ft power boat (RADON) whith a planing hull,Variable deadrise and reverse or turndown strakes.I have twin 315hp yanmar deisels and 220vld close coupled V drives.The proppelers are 21x23 whith a #5 cup.The cruising speed is 20knots @ 2800 rpm.She weighs about 15000lbs.I have been hearing alot about tunnels or pockets and thought I would ask if this is a good idea whith my hull design.I will be adding 4-5 ft to the stern of this boat and figured now would be a good time to put in pockets.The reason for the add on is that I switched from stern drives to V drives and lost fishhold space to accomidate the transmissiones.Also she has always ridden whith the bow high.I run whith the trim tabs all the way down.Any advise would help.Thanx in advance.