With regard to your question about the air vents, you might try a caravan spare parts outlet, which should have them in various sizes for ventilation of enclosed refrigerators and LPG gas bottles.
Hi, This is a modified box trailer. The whole aim of the project was to keep it light and a low profile for towing. I have had it for about 15 yrs and am very happy with how it tows. Cost wise it was about $300 on top of a standard box trailer, that was the cost of materials as I did all the work myself.
Essential but functional and cheap! I am fine now with my roof rack but now that my wife is starting bothering me about 'her' rig and 'her' sail I should consider that too. It's a shame as I live 5 Miles from the beach ...
Pssst Its coming to Inverloch on the 8th /9th January. We are awaiting "Official" wording from JP and NP but until then we are calling it "Caravan of Horror"
... but watch this space - I suspect you'll hear all about it soon! 
