bumper mount bike rack

If you do that make sure the top of the bike is secure so it doesn't sway back an forth at all. NOT ONE BIT!
It's the constant sway that fatigues the metal not the weight.
I bolted a metal bar on the back of the trailer to the top of the bike rack. It's solid, no problems in 1000s of miles

I often haul a 2 bike swagman rack on the back of my TT, but you have the make sure the bumper and hitch can survive torture. Not all bumpers, in stock form, can survive. The back of a trailer is the worst place to mount almost anything. Its a rough life back there!!!

Also, check the bike rack warranty. Many are void if on the back of a trailer. The bounce is very different than the back of a vehicle. Any bumps, railroad tracks, cause an up and down motion that is pretty radical. I went thru two, fairly expensive racks that broke welds; and these 'were' warrantied. I stopped carrying bikes all together. As has been stated, if you do carry, make sure you have very solid structure and a very strong bike rack.

I have a bike rack on my 1999 TT. I carry two full size bikes on it. I was told to make sure the bumper is steel and not aluminum. Mine is steel. This could be because of it being older. I did not take the bikes on the Alaska trip this summer.

They advised against it because the bumpers are so flimsy. I would never do that, get a receiver hitch mounted to the frame and put a bike rack there.

Be very careful about mounting bikes on the bumper of you TT. TT bumpers are thin and not structurally sound. They are not well supported. The bouncing and torquing of bikes mounted to the standard TT bumpers is asking for trouble.

If you must rear mount your bikes, make sure that the rack is welded and or reinforced directly to the trailer's frame members...not just the square tubular bumper.

Reinforce the bumper and it will be OK.
In this pic you can see where a piece of 2" angle iron (part is cut at 45 degree angle) spans from under the frame to under the bumper. Have a welder do this and it will keep the bumper from rotating downward and tearing off. BTDT.