Thanks for all the compliments folks. I've decided not to use it for poultry after all, but am going to hire it out at weekends as a compact and bijou holiday caravan instead

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The base was a very old 6x4 box trailer, so the bits of metal that had been in contact with the wood were very rusty where the wood had rotted and held water against the metal. The rest of it was pretty good though, so it was easy enough to grind it back to good solid prior to rust treatment, welding and painting.
Those ventilation grilles are very cheap to buy, and I prefer them to just holes with weldmesh because they keep out driving rain / snow, but at the same time allow for good air circulation.
It would tip up if you stood right at the back, but in reality it's small enough that I won't actually need to stand inside to clean it, since I can reach right to the back with a hose and brush. Well, that's the theory at least.
HGL - I'll try to get a photo with either Mrs Womble or a team of ducks saddled up to pull it along later

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