Just chop it up into small bits and map them then combine it to the best you can, using simple projections (planar and cly's) its a long process and its a hard slog, just keep at it you'll get there.

Therse a few tuts on Autodesks site that will help out have a crack at them.

This might help too https://www.uvlayout.com/index.php?op...pper&Itemid=72 , its a trial of headus and its a really great tool, just as with a lot of things, dont rely on it to do the work for you, you need to know what you want out of it,