I'm about to brew my 1st trippel, and was reading up on the style and liked the article on trippels in last months BYO magazine.
From what I've read, Belgian Trippels are usually much dryer ... and may use 15%-20% sugar for such. Your FG should be lower.
The style should really be about the fermentation control, and the grain bills are usual very simple and light on 'charcter grains'... maybe 5%.
Of course, if you are going off the brewer's ingredient list, in order to clone it, then follow his lead. I'd just think about your FG and try to keep it dry, and control your fermentation temps well! (e.g. start low-mid 60's, and let it slow raise over a week to 70-F)
But, I am a n00b Belgian brewer... Follow your gut!
Good luck! I'm brewing mine at the end fo the month!