Belize travel reco -- if you do go to Guatemala, immigration and customs on both sides is a total CF, especially if you have a car.
But most important -- make sure they actually stamp your passport upon re-entry on the Belize side. I'm certain it is a scam, but my passport was not stamped upon re-entry even though it was with the 4 others that I handed immigration. I got a pretty good shake-down at the airport with multiple threats of me having to go back to the Western Border station to get a stamp. That's a solid three hour drive, even if I did have a car, which I had turned in days ago. They knew that. Turns out - shocker - that a cash payment for the missing stamp would be accepted. And conveniently, there was an ATM right outside the shake-down office. It was $200 Belize, which is about $100 US, so I readily paid. That's probably the sweet spot for getting some cash and not causing enough trouble to get US state department attention.