Nice one Eric. F/11 certainly isn't going to give you a wide field of view that's for sure.
It's would be like imaging down a drinking straw after using your f/4.
Yep, hartmann mask or diffraction strings across the dew shield for focusing will help, but if you are only guiding with it absolutely correct spot on focus isn't necessary as your not going to be processing it. Your stars still need to be focused but you don't need to be pedantic about it.
I use another option for getting within the ball park, especially as I may be swapping things around during the night on my refractor. For each item I might be attaching (300D, ToUcam, ToUcam and barlow, Eyepiece projection, DSI etc) I have a line marked and labelled on the focuser tube to save me searching for focus. I'm in the process of doing something similar for my SCT on a label to be attached to the side of the OTA. But not being able to see the mirror distances change I'm using 1/3 turns CW or CCW from focus on my 12mm reticle. Seems to be working Ok.