What the guys have said so far it true. I've owned both, a Tri-Wing 05 RSV converted by myself and currently own a 09 w/Hannigan converted at the factory. 
After it's all said and done the Hannigan will cost 2 to 6k over the cost of a Tri-Wing depending on options with either company.  
I love the ride of the Hannigan as does the wife. A solid axle will jar you more on rough roads. I believe handling is better for the Hannigan as well as the lower, wider & longer wheel base hugs the roads better in twisties.  
I did put over 35,000 miles on the Tri-Wing up until last fall when I got "T"boned by a cage and enjoyed ever mile I had it.  
I've got a whole bunch of pics of both conversions with the bodies off I can send to your e-mail if desired.  
Larry 
BTW: I'm a retired mechanic as well and did build the Tri-Wing doing it all but paint. 
 for the same reason you mention.