Can anyone recommend a handlebar mounted waterproof map-bag for some epic off roading with map and compass?

not much experiance here Terry T , but a suggestion is to get map on cd rom print out relavant sections and laminate , if you already have maps (paper) then perhaps digicam them and as above.
An idea probably a poor one but I tried!
Must say I thought you were very good in school for scoundrels ;¬)

MBR did a test of them a couple of months ago.

Have a look on the wiggle website. There is one there under handlebar bags. There are also a few handlebar bags with integrated map cases. They are expensive but if you are going on a few epic then you coul probably use some luggage space.

To be honest though I'd probably stick to something simple like an Ortleb map case at about £15 and stick it inside my jacket if I were you. That's certianly what I do when I need to get the map out to navigate.