To keep the wires as short as possible, I would suggest starting it at the top of the silo, then run down the center and then out the side. You will likely want to run this electrical wire against a length of rope wire like they use to support small antennas. This will take the stress of the electrical wire when the time comes to empty the silo.
As mentioned before, you can get any type of display you want. Anywhere from old analog needle displays, LCD/LED displays like in a digital voltmeter or fever thermometer, all the way up to a display on your laptop.
Again, much of this will depend on your wallet and your skill level. I suspect that industrial companies all ready sell such a system but a a steep price. Grain silos must measure temp and humidity to keep the grain from spoiling.
On the cheap, I would experiment with a 50' length of cat-5 plenum cable, a thermistor, and a voltmeter. The thermistors are dirt cheap (see http://www.sparkfun.com/products/250
). The cat-5 plenum might run $200 for 500 feet. Each cat-5 cable has 4 sets of twisted wires. That would give you four sensors if you keep a seperate ground for each one (likely a good idea).
You will need to learn to solder and dress your connections with shrink tubing and a good strain relief.
Now you can simply measure the resistance from the other end of the cable. Now you compute the temp from a table or equation. If this all works, you could try your hand at a small device to display the temps for you in whatever way you want.
Gave you give us an idea of your budget and skill level?