The general concept is that if you buy items that have an expected useful life of more than 1 year, they are assets, and you deduct the cost over the expected life of the asset (which might be 5, 7, 10 or more years, depending on the type of asset.) Individual items that cost less than $2500 can be taken as an expense (basically, to save paperwork, so business owners don't have to track every small item). And there are a couple of special ways to deduct the cost of the asset all at once, or faster than the regular schedule, but you don't qualify based on the type of business you will be in. (And even if you did, there are tax consequences if you stop using the asset for business before the end of the original schedule.)
So yes, you can "write off" the cost of a trailer, but as an asset over time, not all at once.
