One thing I'd recommend doing is actually typing it in the "reply to thread" screen and copying it over to a word processor for transport and for editing when on the go. I do this pretty regularly, and I haven't had problems (yet) with it changing my quotes to question marks. One reason it might be doing this is the forum's font doesn't recognize quotes and instead substitutes them with something it can recognize.
What I did for my last post was write it, block by block, as a private message and then send it to myself. That way, I had my written material saved in a format that would be transferrable, and that way I could edit it at my leisure (though be warned, it seems that PM's have a smaller word limit than actual forum posts).