I ran a backhoe for a living for many years, and now have a Woods hoe for my Boomer 35, I have never got off of the machine to move down the trench, leave your FEL up, park brake on, lift your stabs up a few inches off of the ground, lift the rear wheels of your tractor machine with the main boom of your hoe, and move forward with the dipper, even with little experience, you will be able to trench 300 yards 12" deep in very little time, plus get a bit more time behind the hoe, you will be well experienced in an afternoon. If you are sure to leave your stabs only 3" off of the ground, and take your time, you will get the knack of moving the entire machine without ever having to 'drive' your tractor, make sure you straighten your wheels before you move, and with a bit of practice, you will be straight trenching in no time.
regards