Your right about the lights, but the customer after being informed wanted a full set. "just to look cool".
Some barges DO have a full set of lights. Towing, the tug must have a full set (red, green, white) plus a yellow tow light on the stern.
As to tires I get mine on E-bay or at hobby shops. Take a look for model car tires. I have purchased mixed bags that include 1/32, 1/24, 1/12, 1/18 all the way upto 1/4 scale. I usualy get 6-20 out of a bag of 30-50 and prices run from $ 6.00 - $ 30.00. That barge I built has 3 differant size tires on it.

Most people on ebay only ship inside US for some reason.

proteque check with your hobby shop to see if there is a plastic modelers club in the area. Model car builders will almost always have extra tires around. You might be able to buy some from them.

A good source of tyres in UK at least are the "Charity Shops" plenty of broken toy cars, trucks, tractors etc usually for a few pennies. If you want to buy from UK try www.redbankmodels.co.uk They have them in various sizes , about 50p each though. Is there no Norwegian Ebay ? One other point , the blunt ends on your barge could be improved by cutting the square to a triangle, i.e. a 45 degree slope for less resistance. I think also another load area/hold to match the one you have. It would be a nightmare with a load at one end of the barge and empty at the other ! Otherwise A-OK , keep building.

Same barge, new load, black aquarium gravel, pour epoxy on blue foam and pour in gravel, works well.

wow. thats nice!

I tested mine today if it floats like I wished. and success it floats exactly like it should. so the self balasting system works