The last vehicles in and out of the race track paddocks, the most cantankerous, the most neglected and the ones that can ruin a weekend before you get to the track or on the way home afterwards. The longest owned, the ones most often parked outside, the ones with the dodgiest wiring, the most rust, the oldest most cracked tyres - especially the spare which will have been there since Adam was a boy - and the rumbliest wheel bearings the most absent wheel nuts. The ones with the cheapest annual rego that don't always behave going backwards. The most often lent and the most abused.
Take a walk around the parking area at any race track and there will be a very mixed bag of them sitting there, some basic, some repurposed, some sign-written a few deluxe. Two wheels or four, trailers are as an eternal part of racing as Flag Marshalls and ear plugs.
Have you ever noticed a weird disconnect between the value of the bike and the condition of the trailer beneath it? Often the most desirable and rarest machinery is conveyed on something that looks fit only for the scrap heap. There is also often a disparity between the vehicle towing and the trailer, a new top of the range 4WD towing a trailer that seemingly survived the invasion of Stalingrad in WW2.
Trailers evolve, get repurposed, get forgotten, reborn - they are as close to an immortal vehicle as a child's metal scooter. Provided there is some rust and paint in approximate contact they endure like Grandpa or Grandma's axe until one day they just vanish.
Wheels can be lost enroute, the last time I saw this was off a boat trailer where the wheel ended up knocking on the door of a house having jumped the garden fence. No harm done, not unexpected, it happens., "That's trailers, mate."
Do yourself a favour, grease or replace the bearings, check the wiring, wheel nuts and tyre pressure at least once a season before hitting the highway to save yourself coming to rest on a hard shoulder, in rain, at night, miles from BuggeryDoo. And if it still happens to you after all that preparation, "That's trailers, mate!"