HELP! Experienced guidebook writers?

HI! I need advice. I have the chance to submit a proposal covering a foreign country for a well-established guidebook company. I've written for all types of online guides, but never anything so detailed and comprehensive as an actual guidebook.

SO: has anyone here authored an entire guidebook? What is is like? Utterly thankless, or mostly worthwhile? How about a guide to a foreign country that isn't your residence?

Here are some other concerns:
--I'm not sure yet if I'm allowed to take comps (I can for About.com; see my signature). If not, I assume travel costs would have to come from the (high four-figure) advance.
--The foreign part: it's a developing country, and there are plenty of unpaved roads, sketchy/rural regions, things like that. I've been there a number of times, but not to EVERY nook and cranny.
--Thus, because I'm a young woman, I'd want travel partners in most places. (Wanna come? j/k)

Any tips? Advice? I have to submit the proposal in two weeks including a portion of a sample chapter, so I want to make a decision quickly. Thanks!

Thanks, guys -- very empowering I just found out I am allowed to seek comps to help out with research costs, so I'm going to do it (the proposal, at least). If anyone else has any experience in guidebook writing, I'd still love to hear about it.