I saw this in an ad last night. Off is making a small powered mosquito repellent device that takes replaceable inserts and clips on or can sit next to you. Seems like it would be great for tarp users, hung from the ridge line.
Of course, the weight isn't published and it takes 2 AA batteries, so it's not going to be featherweight. The toxicity needs a good look too. The active ingredient is metofluthrin.
http://www.off.com/clip-on-mosquito-repellent/
PDF on metofluthrin toxicity:
