For slow rolls, there's no getting around the use of rudder--you have to do it. For horizontal rolls (as opposed to upline & downline full & fractional rolls) less than three seconds, I sometimes do and sometimes don't...not because of any deliberate calculation, but it depends on the plane I'm flying, whether I'm goofing off or practicing seriously. I seem to have acquired the habit when rolling from inverted to upright of boosting the tail with a little of same rudder to aileron. When I'm concentrating, I touch in opposite rudder rolling from upright to inverted.

When I do a high horizontal roll and I think the judges can't see any better than I do, I will often try to get away with just elevator correction, no rudder. That's probably because I'm thinking that if I use rudder at and don't do it right, it will be more noticeable than if I just leave the rudder out of it. When I took a series of classes in Intermediate, my instructor recommended elevator only, so that was my excuse. At that time my inclination was to slow the roll down enough to touch in the rudder. However the drill was double and triple continuous rolls, and the concentration required to time rudder and elevator for a triple roll was more than my synapses could handle. Triple rolls take lots of practice (like everything else in pattern!).

If I'm doing a low horizontal roll, I feel I have to use the rudder but I usually practice that with special attention before a competition. If you check the Don Ramsey Pattern Page http://www.cox-internet.com/donramsey/index.htm and click on Flying Techniques I think you'll find an authoritative recommendation for using rudder in all horizontal rolls and fractions.

Next consideration is the use of differential on the ailerons. For a while I did not see the necessity for doing this. I'm not sure it's included in the NSRCA trimming procedure. But anyway, the test is to fly straight out or straight in, wobble the ailerons and see whether the plane wobbles left and right in the yaw axis in addition to the roll axis. If it does, then it will also wobble (noticeably!) when it rolls through the quarter points. Program in some differential on your tx to take this out. Obviously this correction will reduce the amount of rudder correction you need.