I lack the technical skills to do the wiring myself.
No you don't. If you have enough fingers to type your post and enough intellect to be literate and able to use the internet you can handle this job. The power cord is not shielded and you only need to extend the red and black.
There are a couple different ways to go about it, but the easiest might be to just make an extension cord for summer rather than cut and lengthen the wire permanently. Get as much wire as you need, something around 20awg should do it and can be had in small packs at home improvement stores, or by the foot from auto parts stores. Then get some spade connectors that match the size of the ones that come on the power cord. Cut your wire to desired length and strip about a 1/4" of the insulation. If you don't have a stripper just use a sharp knife or razor to score the insulation and then pull it off with you finger nails. Then you just need to put female connectors on one end and male on the other. The connectors need to be crimped but if you don't have one you can use pliers or a hammer.
The really easy way is to skip the crimping all together, cut the stock harness and use screw caps or tape for the connections. It will work but be half assed and not the way I'd do it.
If you are lacking the tools and required parts literally everything you need(wire, connectors, stripper/crimper) can be had in cheap kits for about $10 bucks at any hardware/auto store.