No Barlow needed. In fact, a focal reducer may be more in order. M42 can be a larger target than most pople realize from the visual view they get in thier scopes. Going with a wider field will allow longer shots than otherwise possible without tracking.
I would suggest maybe ISO 800 or 1600 and try 30 seconds. If the stars start to trail, shorten the exposure to say 20 seconds or even 15. If not, see if you can go to 45 seconds. (I really doubt you will get any longer shots than that.) That's the beauty of digital photos. If you don't like them just delete them and try something else. FYI: ISO speeds higher than 1600 will introduce a substantial amount of digital noise into the image. You can try it, but just be prepared for the grainy results.
Denham Springs, Louisiana USA
"Second star to the right - Then straight on until morning!" - Peter Pan
Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars