I have an oasis and I located my outriggers a few inches behind the back seat. They will work the same in the middle or tward the stern. I started to mount them in the middle but since mine has a cross bar, it would not work in the middle because could be uncomfortable for my front passenger when leaning back.
I had the same challenge with reach, so I found that useing a backing plate as an outter template to drill the holes, then threading some stiff wire through one of the holes, the backing plate can be attatched to the wire at a hatch and pulled into place. One tip is to place bolts/screws through plate in each hole as they are drilled so nothing can drift. Then there is perfict alinement.
If your plate dosent have molded incerts for the nuts, you can make some from strips of plastic cutting board with a hole just large enough to catch the points of the nuts. Tap in the nuts, line up on backing plate useing bolt as a guide, then use 2 short ss screws to attatch strips into place.
Then once the plate is pulled into place by the wire, keep tention on the plate and use something like an ice pick in the other hole to line up the other nut by manuvering plate back and forth. Run in bolt but not tight, then remove wire, and use the bolt to line up other holes and nut, run in other bolt, then tighten down.
That is about the best I can explain it, but it works very well. I did this for my outrigger brackets and handles on my Oasis useing plastic cutting board to make my backing plates, and all worked out well.