AFJES,
Bear in mind that you will be working with 2 entirely different hazards here.
The first being voltages of up to or in excess of 50kV, depending on the size of the sign.
I've worked on relatively small signs of 18' x 6' and they have used voltages in the area of 40-45kV.
This is not something you want to mess with, if you can avoid it.
The second hazard is that of the fragility of the neon tubes themselves, while they will be braced to a certain degree, during the moving of a lighting install like this, if a crane operator bangs the box against anything, it is usually "game over", the tubes after having been used before, become more fragile.
Personally, I would get a speciallised sign company to do this for you.
And let's get one thing straight here, it is NOT an admission of the fact that you can't do the work, in this situation, it is more like you need speciallised help to effect the desired result.
