Duh! He's going to be towing, do you really think he'll notice the slightest difference in the steering a bouncy fork might make?
Maybe it's just me, but I find even very slight changes in fork length can feel odd. I put a 415mm A to C fork on a frame that should have had a 390mm and it felt awful, so even a short travel 60-80mm suspension fork will be more of a change than that.
I don't think the towing/bike seat will effect how the steering feels, especially with regard to wheel flop - which is what you can get if you increase axle to crown length without making other changes.
Duh!