Is the ARF already set up for mounting the servos in the tail, or are you just cutting holes into the fuselage to mount them?

If the latter, then you can just glue lite-ply plates on the inside where the servo mount screws will go.  You can make them about 1/2" wide and about 1/2" longer than the servo cutout is wide.  You'll also want to make lite-ply doublers where the servo screws go through.

These lite-ply plates and doublers will both reinforce the cutout area and give the servo screws something more substantial to attach to.

Please reference the attached diagram...