I've had a lot more time and miles on my TowPac equipped 2005 650 since I said the two were not compatible.  The following is from conversation I had with a new convertor:

"I know absolutely nothing about the 400, so I can't really comment about it any further. I personally doubt that any of the bolts supplied by TP will break if properly installed and tightened. As to the other problems mentioned, I also believe that the majority of the troubles are caused by folks trying to make the unit absolutely rigid. I bought my unit used, and found that the previous owner didn't like any leaning or road crown effect and had the right side adjusted so tight that I couldn't get up a slight rise in my driveway because the driving wheel just kicked out stones. I'm fairly sure that had I ridden it much with that setup I would have damaged the mounting bracket that you've read about. Since finding the setup that works for me, I now have put on several hundred miles with no additional noticeable deflection in the bracket. Another possible problem for us old time bikers is taking corners too fast. It doesn't take much speed to lift the inside wheel and put a lot of stress on the outer one. I have changed my opinion on the TP being unsuitable for a 650 if carefully installed and the "trike" ridden appropriately. It's not a true trike and doesn't have the best suspension, either on the Burgman or the TP. I also have no experience with two up riding, so the extra weight may be a factor. My trim 260+/-# does quite well though.<G>"

and:

"The proper setup and down force adjustment is CRITICAL for a good ride and preventing damage to the bike's mounting points. There are lots of opinions on the setup, mine being that the outrigger wheels should have the minimum contact pressure that will keep the bike upright. Others feel differently. There will be a period of trial and error, so I suggest that you NOT install the fenders until you are happy with the way the bike rides."

My apologies to TowPac.