Nice pic Norm , how did you do that ? Anyway we are in the bridge camp , i'm interested why you want to keep it aft Greg . We have a W28 with the main sheet traveler on the bridge ( did all 28s' come that way ?) . I was told a long time ago by Bud "don't mess with it , it's like that for a reason ". The reason  being if it's on the bridge you don't so much need a vang . We have one (vang) but use it more like a preventer  but it also works well as a vang .

You should still have a vang with the bridgedeck traveler system. When the winds are up and you need to jibe, it's better to use an outboard vang to help the boom across instead of allowing slack in the mainsheet and letting it cross through by sheeting in and out again. Also helps with sail shape when running downwind, by flattening the mainsail. Once the boom is all the way out, the mainsheet will no longer be useful since the sheeting angle will prevent you from controlling the boom. Hence two separate vangs to control the boom for downwind sailing. Ultimately I would run four control lines. Mainsheet, outboard vang *2, and the preventer attached at the end of the boom and led to the bow.

I see the biggest problem with the bridgedeck being with hands or bodies who intercept the travel. If you are not careful with the traveller line you can injure someone. Much less likely using end of boom sheeting, but there are other issues related to it.