Since military electronics is my 'thing', I can help some here.

If you really want to protect your PIC:

Use only 4 or more layers in your PCB with one solid layer of GND, and one layer for Vcc.

Use an on-board regulator (either linear or simple switcher) and feed your board 12V or so.
Protect the input to the on-board power supply with a 20V (for example) MOV. Use a series 1Amp rectifier at the input to protect against reverse polarity. Use a 10uF 35V cap to GND between the rectifier and the regulator.

Put a 7V MOV across the PIC power supply.
Put a reverse-biased diode (1N4148) across the PIC supply.
Use a couple of 10uf tatalum and 1uF and .01uF multi-layer ceramics right next to the PIC for supply bypassing.

Put your Xtal very near the PIC. The same with the 22pf caps.

Keep all wires going to MCLR very short. Use a 4.7K pull-up to Vcc. Put a 100 pf cap from MCLR to GND (If you use more than that, your programmer may not work).

Use a Schmitt-trigger gate (74HC14 or equiv) on all inputs. Put a 2K resistor in series and .01uF cap to GND on the inputs of the gates (unless you need high speed).

Buffer all outputs with ULN2003's or 74C7007's or diode-clamped and current-limited 2N7000's.

I know you might not need all this, but doing things this way will guarantee operation in the harshest environments. I have pictures of circuits running at -73C and +105C, and taking indefinite numbers of 15KV (human body model) hits. We have not failed a military test yet, and we have been through lots and lots of them.