Regardless of the band I use a 3' counterpoise wire for the "ground end connection" at the tuner but know of several ops who simply mount the tuner as close to the antenna end as possible and then mount their /p rig within inches of the tuner so that no counterpoise is necessary - they utilize the ground side of the coaxial cabling to provide a counterpoise.  I rely on a short counterpoise wire 'cuz I employ a /p rig that is larger (e.g., a K1) than an MTR or ATS rig.  In any event - lots of wire for the band of operation works well!  I've been on numerous SOTA activations from southern Utah summits and work in to EU countries routinely on 15/20 and 30 with that set up.

72, Jim Rodenkirch