I'm looking to customize my car, but I'm third world country, Serbia, so money and on line ordering is an issue..so I'm looking for experienced advices how to make my PC.

I was thinking about 3 builds:
1. Tablet dismounted and put inside central console.
+touchscreen, can support sim card, can sustain shakes and bumps, GPS, navigation software...
-no USB, limited memory..
2. Lap-Top dismounted, placed in custom case.
+stable power from own charger, large memory, windows..
-no GPS..
3. True PC, all custom case, power...
+can be upgraded..
-parts are off limits for me so PSU and all power thing have to be custom, but I have no knowledge to do that..no GPS, no WI-FI..

So by this I think Tablet can be the best solution, but small memory is worry to me..

I would like to think of some Lap-Top build, some 8'' lap-top, incased, than from eBay:
Touchscreen foil
something like this.
Lap-top has battery so voltage fluctuation is not in question.
and if anyone can tell me where to find GPS for lap-top?
What do you think of my thinking?

I have opening of 19.5cm (W) 11cm (L) it can be customized to 20.5x19 cm.

My calculation is about 200-300euros for all. 100-150 for used lap-top, 50-150 for GPS antena and touchscreen foil.