Where to put generator in 21' travel trailer

I did a nice job of fabricating reinforcement on my rear bumper, even adding 2 inch angle iron on the 7" I beam of my RBS225 Shawdow Cruiser. I bought an Harbor Freight aluminum carrier and surrounded it with a U shaped 2x2 inch tubing and used three bumper mount 2x2 receivers that are attached by u bolts that come with the three hitches. I added two trays on the ends of the top of the bumper for two 95 amp AGM batteries and mounted the spare on it. The Champion 2800 generator sits on also. I have never got the trailer to pull right. I have two friction sway bars in addition to the two torsion bars for lift. The best pulling is with a full tank of gas and extra 5 gallon water cans in the back of my Suburban, that is when it pulls the best, if I stay at 60 mph or less. More than 60 or if a medium size truck like a U Hall comes by it sets up oscillation back and forth to I have to nearly slow to a stop. I have a theory that the slick bottom of the trailer acts as an airplane wing and lifts up on the trailer and that is when I have the problem. I have been tempted to put the $100 mud flap in the hitch across the rear of the Suburban to break up the air stream under the trailer.