Yes, you can see that this mount is a bit "oversized". This because I really hate to see my GPS unit floating around my car deck (and also because of a project mistake, but I tried it in real situation and after all I'm happy with it). It's make of tough material and I hope it will survive for some time. The design is inherited from the one you can see in the shop, but obviously material aren't the same and also the "under the hood" construction.

Before starting, let's say a thing. Sure building this mount was a really huge work for me that I'm not used to needlework, and the amount of time spent was noticeable. So, especially if you hate losing time, consider buying the original one, it's faster and the result is guaranteed.
This this started as a try of building something cheaper than the original, but after all it was not so cheap (I mean time, not money). Remember you'll need a huge amount of sew work. I had e female effort for this :)

But the satisfaction...

What you need: The material list is not long. Substiantially, you need the following:

• The upper layer material: this must be a tough material, with resistence and a nice look, since this will be the side you'll look at. To obtain this material I purchased an ankle gym weight and disassembled it. I obtained two results: first, the material, second the right measure for the unit. More cutting was needed anyway.
• The middle layer material: to guarantee that the mount be capable of resist to vibrations and accelerations, we need that the middle point of the "cross" will be capable of a certain inertial resistence. So it's not possible to have only the upper and lower layer. This isn't enough. We need something in the middle, hidden to eye, that will resist the travel assaults. I choosed to use a thick felt layer, cross shaped to fit into the outer layers.
• The lower layer: this must be a hi-grip material, because this will be in contact with the car deck and must resist all kind of accelerations (within certain limits...). I obtained the material from the previous cited gym weight (the inner layer, the one that usually touches the body skin).
• The border material: Obtained from the same gym weight.
  
• The weights: to be sure the mount stay attached to the ground even under our offroad trips, we need to anchor it by gravity force. So we need four weights to be putted at the four arms of the cross. To obtain a good weight, capable of a little deformation (it's nicer to touch and easier to work with) you can go to a fishing shop and buy a Kg of lead speres, about 1mm diameter. You can assemble it with four little plastic bags, not too tied to permit a good manipulation of the weight. I assembled four 300gr weights, so I needed 1.2Kg of material. Perhaps 300gr is too much but this was my choice. You may choose to recycle the gym weight material, but I choosed not to do this because it was something like sand and I didn't like that.
• Screws: our aim is to attach the bundled plastic car mount to our work. We'll need to disassemble the plastic car mount by unscrewing the four little screws that we can find to the bottom of the mount and by substituting them with new and longer screws, since we need to go through all the three layers before goin' into the plastic unit. I suggest finding something with flat drill, flat head (wood screws are good, just cut the drill) and 2/3mm longer that the original one. Consider that the three layers can compress when screwing through them, and the screw cannot be too long because it may damage the plastic unit. To avoid that the screw head to break through the layers material, we need also some metal rounds.
• The original material: sure this will not work without the original plastic material bundled with the unit. If you already used it, consider avoiding to proceed, since the cost of buying another plastic mount will not justify the work. I choosed to use also the repositionable sticker to guarantee more gluying of the plastic mount to the upper layer.

Let's assemble it! To the left you can see a little schema that may help you understand the whole thing. Please note that the weights are over the felt cross, to give more stability.

The assembly steps follows:

• Sew up the lower and the middle layer, to guarantee that the felt cross be the more possible glued to the grip layer.
• Sew up the upper layer, leaving room to insert the weights. You achieve that by sewing only the center of the cross. It's important that you sew the center of the cross, since this give more robustness.
• Insert the weights and sew up around them to enclose them between the upper and lower layer. If possible avoid sewing also the felt cross, left it inner.
• Finish the sewing work by sewing up the border to hide the dirty work.
• Unscrew the original plastic mount and attach the lower disc to the work by the repositionable sticker. Use it as a measure to drill the three layers with the new screws.
• Using the new screws, finally close the plastic mount (pay attention to the inner elements). Remember to use the metal rounds to give more resistence to the assembly.
• Last, but not least, remember to put something on the screws head. Sure you don't want to ruin your car deck after all this work!

On the right you can see some details. In particular, notice that I attached the plastic mount a little tilted respect this ideal position, to obtain a better access to the two levers.

Ok, we made it! Now we can try it out. I hope you found this how-to useful. Please let me know. You can find my eMail address somewhere around the site.

Enjoy!

The plastic mount has been tilted to guarantee lever operation

The back. Notice the sewing work and, in evidence (yellow) the four little grip material patches that cover the screws heads and metal rounds.