this may be old news--but www.motortrike.com is now producing conversion kits for rocket 3---they call it rocket v. $7,000. --you install/paint. factory in east texas.
One way to spoil a good bike , here in the uk with all the traffic on the roads , two wheels allows you to make quick and easy progress 8) , 3 wheels will be no good , might as well be in a car . :?