Denise, from the pic, it looks like your rudder will stall out rather quickly.. Having done a bit of river sailing myself, I know what you mean. Gaps between buildings can be unpredictable at best!!
Forget the traveller - I found that the best thing to do in a gust (especially in a race) is to have someone ready to dump the mainsheet and able to get it back in almost as quickly. The best system I've seen for this is one with "coarse/fine" adjustment for the mainsheet: basically a 2 or 4:1 purchase with a 12:1 or so on the inboard end for getting the mainsheet in hard when it isn't so gusty. It may mean a couple more blocks on the mainsheet, but if it makes life less "interesting", I think it would be worth it..