Trailer hire help needed

I am a leader for a scout group in Dartford, we are taking 30 kids to France on 25th July for 8 nights. Our plan is to transport all the kids and leaders in 2 x 17 seater minibuses and one of the other leaders will drive his car with a trailer in tow for the luggage. This is where there problem starts, most trailer companies prevent there trailers from leaving the country or they then demand an extra high rental cost for doing so. Does anyone have any experience or advice on this?