Weight is weight. It dosen't matter if it is a couple bikes or a box full of gear. The problem is the reciever cargo hitches are a fulcrum on the bumper of the trailer. I though about doing this when I first bought my trailer but have had second thoughts since then. I had a similar setup on an ATV and it caued too many issues. I am however quite certain that I could fabricate a carrier that would work. The frame would have to be reinforced, etc. Just not worth it in the long run and I would prefer to keep my frame warranty intact.
On another note. It is very common to see the "triple tows" here in my state of Wyoming. Personally I would not do it, but many do
2012 Grey Wolf 19RR
2008 Dodge 2500 CTD
Nights camped 2012 - 35
Nights camped 2013 - 46