I have the double TI trailer and I understand the only difference is it's 9" wider cross bars (8' wide), same length.
Also, it seemed, the TI trailer was a LOT more expensive than the AI trailer. My dealer was told it was because it included both crossbars (AI & TI), but if it did, Trailex then shorted my dealer his AI cross bars for his AI trailer ordered with it. Also, the shipping was 4x what was quoted by Hobie, again, supposedly because of the extra set of longer bars. For the 9" difference, I think I could have made due with the AI double trailer.
It is a nice trailer, well designed, and assembly (I assembled it) was easy once I found the CD included and printed out the instructions from among a dozen files.
This is a big help. Thanks for the info. It sounds like the best decision for a TI and Adventure (not AI) would be the Double and if I ever upgrade the Adventure to an AI, I may still have enough width to make it work. I don't have pricing on either trailer yet, but it makes sense that the smaller traler would cost less and shipping would be lower too.