In my experience, mesh won't give adequate protection from the mist produced from condensation and it makes sense to take some kind of bivy bag protection. Unfortunately the RAB ultra doesn't seem to be available, nor the equally light Equinox bivy bag. It's probably too late to order anything from MLD.

Addendum: the RAB Suvival Zone Lite weighs 236g and might be worth a look http://www.ultralightoutdoorgear.co.uk/rab_survival_zone_lite,_ultralight_bivi_bag.html

Cheers for all the opinions folks.

I have decided to make an enquiry with Bearpaw Wilderness Designs re: a solo inner with ripstop on 3 sides and a ripstop/mesh combo on the door- will be useful for winter use and save me buying a new bivi bag. Should be here well before the crossing!

Stuart