Here's another interesting method of perfboarding, this guy does it with SMD components and really tiny wires. He made a special little wiring pen for laying down the wires:
Progressive Wiring Techniques
(source: davr.org)
Personally I make solder bridges for pins that are in adjacent holes, for things further away I use thin wires (though not as thin as the ones above) in adjacent holes to the things I want to connect.
Top of my board:
Bottom of my board:
And no, I didn't just wire those pins all on the fly, I had drawn up a detailed schematic in advance. There's no way I could keep track of so many wires just in my head.
Some useful information about different types of solder: NIST Metallurgy
The main important tables are 1.12 (coefficient of thermal expansion/elastic properties of leaded solders) and 1.14 (tensile/shear strength of leaded solders).
I believe the document has information for lead-free solders as well (that is what it is called after all), I didn't look too hard for these.
The key properties for 63/37 leaded solder:
Coeff of thermal expansion:
$$
\alpha = 24 \frac{10^{-6}}{K}
$$
Elastic Modulus (I'm using the 20 degree figure, it will be slightly higher near 0 degrees, not exceeding 38.1 GPa at -70 degrees):
$$
E = 30.2 GPa
$$
Tensile strength:
$$
\sigma_{max} = 56.19 MPa
$$
The worst case scenario is if the solder is mounted onto something completely rigid. Suppose we were to take the 0 stress state as room temperature (25C).
The contraction due to thermal expansion is:
$$
\epsilon = \alpha (25C - 0C) = 0.0006
$$
And the appropriate tensile stress is:
$$
\sigma = E \epsilon = 18.12 MPa
$$
This is well below the tensile strength of the solder.
However! Even better is that the PCB board itself will contract with the solder as it cools down. Depending on the actual layup direction, this closely matches the 63/37 solder CTE (~20e-6/C for the primary direction), so the actual stress will be lower.
tl;dr: you'll be fine. You might have to worry more about moisture/condensation, as well as having components which are rated for below 0C operation instead of worrying about solder joints cracking.
Best Answer
The answer is... it depends.
If there is any danger the connector may vibrate loose or otherwise corrode and lose contact, definitely go with a soldered connection.
Since the product is sealed, then, on the face of it, soldered seems like the cheaper choice.
However, you need to factor in assembly/labor costs. If your wiring harness is mass produced it will probably be cheaper to include crimped connectors on the harness rather than have someone solder and strain relief the wires to the board.
In a well designed product, the internal wiring is built on it's own on a jig as a harness and simply dropped into the box and affixed with tie-wraps or clips and quickly attached to where it needs to go.
Which method is ultimately cheaper in your application, is, of course, in your wheelhouse, and can not be answered here.