[Swampdude]

It sounds like you're trying to pull a negative pressure on a trailer? One of the questions would be how fast do you need to do it, and what is the desired negative pressure? When you say you want to suck the air out, you really need a goal as to what condition you want to leave the space in. Are you also trying to remove oxygen, or get an inert environment etc?
Any pump/hp will eventually get you to some level of negative pressure, given its required length of time. You just need to decide the time, and the desired pressure - or am I missing something?