I wanted to be able to mount my SLR Photolenses with webcam on top of the LX200 but when I looked how much a commercially available piggy back rail would cost I was shocked :-{
I talked it over with my good friend Matthias Meijer who produced this sketch:

I gave it a good thought and then hurried to the DIY shop where I bought the following material (total costs Euro 35):

With the above material I made a Piggy Back Rail with adjustable Sliders.
Note: guess how am I going to make a Balance Rail :o)
And of course this Piggy Back Rail is interchangeable with my LX200 Heavy Duty Piggy Back Rail for Autoguiding

I bent the drawer handles so that they followed the curve of the OTA so that I could attach then to the OTA using the original LX200 bolts.

The complete Piggy Back Rail with sliders: steady as a rock!
Note: it is nice that all my LX200 Piggy Back Rails can also be mounted on my Astro-3 (Lidl) mount: yes, I like to be able to use my equipment in multiple configurations.

Using pliers I changed the shape of the drawer handles so that the holes match the bolts of the LX200 OTA.
I drilled matching holes through the aluminium tube and drawer handle and used M6 bolts and wingnuts to fasten; by undoing the wingnuts I can remove the piggy back rail while the handles remain fastened to the OTA.
The nylon caps make a nice finishing touch.

The top of the sliders are made of 18mm plywood: 4cm x 8,1cm: the extra millimetre is to provide extra play so that the slider does not get stuck on the piggy back rail.
The bottom is made from 4mm hard plastic ("Trespa"): 4cm x 8,1cm and the U-shaped aluminum strip acts as connection between top and bottom.
The slider is bolted with 2 M6 bolts and wingnuts; inside the U-shaped piece is also an M6 nut so that I can swap the top for one with e.g. a ring mount.
To protect the paint of the OTA the very bottom of the slider is finished with a layer of felt.
I am planning to put 3-point ring mounts on top of the sliders but I have not yet decided about the size I need.

I used a left-over piece of hard plastic to make a platform between the two sliders and mounted my Witty slow motion controller on it.
Using the knobs I can make very small up/down/left/right movements.

Here is my SC3 webcam with 135mm SLR Photolens on top of the Witty.
It might seem not very stable and top-heavy but in fact it is quite doable:
with the same setup I have made many succesfull long time exposures
as my images demonstrate; see for example this image of M31
Meanwhile I have added a Viewfinder.

Here follows a list of all my Home Made LX200 based Piggy Back Rails:
Heavy duty Piggy Back Rail
Balance Rail
Piggy Back for WO ZS 80 ED APO
Piggy Back for Filterwheel + SLR Photolens