I've had two breakdowns while towing the boat trailer in the last five years. I'm with the AA Relay service.
First time collected a boat/trailer from Liverpool heading home & the wheel nuts all fell out as the bloke hadn't tightened them after fitting new tyres
The AA turned up after 20 minutes and arranged to have their flatbed wagon retrieve the trailer which was @20 ft. No questions brought it all the way . Had to wait about an hour.
Second time coming home last year from Kintyre fully loaded the Merc gearbox blew a seal at services on the M6. First bloke in his van probably 15minutes. They then said about an hour which stretched to about 4 until the contracter turned up with a lorry, loaded the Merc & hitched the boat trailer and brought us home. By way of apology for the delay a bunch of flowers and a telephone call giving me free membership for another year
To be honest I wouldn't go anywhere else for the peace of mind !!