I have been towing for years and STILL get nervous doing it. So much can go wrong, even with a seasoned traveller, in a great trailer, great towing vehicle and an experienced person behind the wheel.
Once I was driving back on my own from a very long dressage comp, I'd had a really bad day, been up since 3am, it was a 4 hour drive home. 10 minutes from home, going up a hill, my cars engine cut out and next thing I know I'm rolling backwards. I managed to back onto the side of the road, I had trucks flying past, people honking at me and my horse going ballistic. I was too scared to take my foot off the brake in case the hand brake failed as it was a very steep hill. My horse started to rear, broke his rope and hooked his head around the back of the stallion divider.
Things like this can happen so easily - avoid the stress, get him trucked over. 10 hours is a very long way for a horse to stand in a little box when he hasn't had much experience travelling, and with people that don't know what they're doing.