re-entry permit

Hello,
I have a friend coming to visit in a week and we will head off to Laos and vietnam or perhaps south down to Malaysia for a tour.
I have a non immigrant b visa, with a one year extension. I am a teacher with a work permit. I was going to go get a re-entry permit for when i come back, gone for 4-6 weeks.
Can I get a re-entry permit with out knowing details such as where and when i leave the country? Once you get the permit is there a time limit.
Thanks very much,
marcus

I got a re-entry permit that was good for any number of re-entries during a one year period. Since you work here, this type of permit might be useful for you. It will allow you to come and go as much as you please for one year.

You can also get a Re-entry Permit for just a single Re-entry. No definitive travel details are required - just fill out the form, have a photograph to attach to the form, and pay the fee.

The best recommendation that I can give you is to go to the Airport and speak with the experts at Immigration.

I think in your case the I year re-entry permit at 3800 baht.

Thanks guys. It's a 1.5 hr drive to immigration for me so I just wanted to check first.
Bottom line. They ask on the application when you are leaving where you are going and when you are coming back. I asked the lady, she said it doesn't matter what you write. On the stamp in the passport none of this is recorded. With the re-entry stamp I can leave and come back any time within a year.
Cost was 1000 baht for one re-entry 3800 for multiple entry. I doubted leaving more than four times in one year so opted for the single. After I return from this holiday I will get another re-entry stamp in case I want to do a more spontaneous trip to laos or Cambodia.
The entire transaction took ten minutes at the Khon Kaen immigration.
Thanks for the help guys,
marcus