Well, since you didn't heed to advice for a first plane, I won't say a thing about your choice for a second plane.

Mechanical trim simply involves making sure that at zero servo input, with all sticks neutralized including the trim tabs, that the surfaces are straight and flat with no up/down, left/right in them at all.

The way I do that is:

Before going on, make sure your transmitter, if a computer transmitter, is using an empty model with no mix, no enhancements (dual rate, expo, nothing). If it is not a computer radio, then move on to the first step.

First, disconnect all your control rod clevis’s from the control surface control horns.

Next, center servo’s by turning on the TX and RX and putting the TX sticks in the center, the very center.. not about center, but in the center. Center all trim tabs. This is a real important and an absolute necessity. There is no “about” with this. Get them right. If the servo arms are NOT centered, meaning if the arm you are using is not perpendicular to it’s side or front surface (depending on how your servos are mounted), remove the servo arm screw and rotate them until you find the one that is perfectly perpendicular with the side. See the sketch below. Put the servo arm screw back in and tighten it. All servo arms have one arm that, because of the splining of the shaft, will have one that is perfectly perpendicular to the side or the front of the servo. Make sure you do this correctly or you will introduce unwanted differential. Just push it on and see if it is perpendicular. If not, remove it, rotate it to the next arm and check that one.. do this until you have the right one. Turn off your TX and RX.

Next, make two lengths, say six inches, by four inches, of thin ply. Sandwich the control surface AND the stab/wing then carefully and softly clamp this so that it holds the control surface straight and in line with the wing or stab.

Now, adjust your clevis’s so that when you attach them to the control horns on the elevator/rudder/ailerons, you can do so without moving them (thus the reason for clamping the surface in the above step. Once you are happy with this step, remove the clamps. If you have split elevators with two rods, do one side then do the other side. Make sure they are the same.

Now move on to the next control surface and do this one. When you have all of them done, and have removed the clamps, and

Turn on your transmitter and receiver and check movement. Remember, when standing behind the aircraft, right aileron stick moves the right aileron UP. If it’s reversed, fix it!! This MAY result in the necessity of doing the above steps again. (reverse may cause the deflection to change, so go back to the first step, zero the sticks, zero the servo arms, then re-adjust the linkage.

Once you are done all of this, your initial trim settings should be at zero. You are ready to fly it and do the in-flight trim adjustments.