I can't say I'm familiar with the TowPak but I installed a Danson kit in the spring.  Its run for over three months with no problem.  The kit is amazingly stable and the fat 15" tires are hot especially compared with small 13" wheels on some other kits.  Everyone wants to see the trike and our local bike shop has sold a kit to a Burgman owner after seeing our install.

We have a 650 so there is some body, and horsepower, differences with the 400.  The Burgman is a little more pricey but if you want a good long term investment it's worth it.