to experiment with mounting the bearings on the OTA that way.

A sliding balance weight is another way to deal w/ balance problems and i've seen bearings that were on tracks on the side of the OTA as well.

As far as tube length- i think they do recommend as a rule of thumb a tube length equal to the FL of the primary. From what i gather, another rule of thumb is to have 1 primary diameter of the tube ahead of the focuser's center. Of course, if you don't want a tube this long [for transportation/storage concerns] you can always add a removeable dew-shield.

I suggest you download the 'Newt' program [a web search should find it for you] and play around with that. I've used it and it seems to work well.