a lot of Americans sell up and bring lots of dollars out of savings plans and stuff or selling houses and bring it to Thailand. Then find out they have a large tax liability. I've heard of people that the IRS wants USD$200k from because of bad decisions. It's just a suggestion.
with a non-immigrant long-term Visa he gets a five year otherwise just a two year. I know because I have felt that pain going from five to get back to two.
The normal Cambodian border is a hotbed of issues. People not being let back in. Sometimes having to get down to Phnom Penh and flying back. I would suggest other options for exiting and re-entry.