Why would you tell him he would regret this when you have never done it ? I pulled two bumper pulls for several years and in some very windy conditions as well as other conditions without issue. Also i could back them up in certain conditions if i was patient. I believe the towed pulling a trailer would be even more stable than two trailers as there isnt the issue of trying to properly load the first trailer. If the OP does as i did and check with the Highway Patrol about legality and carries that proof then there is no issue. Think about it, this person is being dilligent about whether its legal or not.