You can always under-load floor space on a trailer, but it always looks funny as hell when you start hanging your mowers off the side and stacking them struggling to fit all the equipment on.
GoldPro is bang on. Buy for tomorrow - no wait - buy for next week, not for yesterday and today. That or buy again tomorrow. (this gets costly) It costs so little extra to go the next size (or 2) up in trailers.