he is saying the trailer requires upgrading due to the lack of weight you can put in over standard.
this relates to the trailer.
"When I bought the storm (and the wing will be similar) it only has about 300kg of loading capacity from empty to its max weight allowable, the water and gas needs also to be included in this so it doesnt allow you much for clothes, food and extra stuff you want to carry before you are illegal. my upgrade added 400kg to the 300kg and it allowed me to include solar panels, and all my gear, fill etc etc"
once you fill the tanks etc, you only end up with a tiny bit for clothes, food, drinks, extras etc.
I'd also still test tow one...