After reading lots of posts, I think what I describe below will work, but I want to check with the kind experts on this forum.

I'll be flying into Bangkok in late November and will be in Southeast Asia 4 1/2 months. One month in Thailand, and then about two months in Cambodia and Laos and perhaps further afield. Then I'll return to Thailand for about another month before flying out.

It seems the best way to handle the visa is to apply for a 2-entry tourist visa at a Thai consulate here in the United States. Is that the easiest way to do this? And will airlines accept that so I don't have trouble boarding since the arrival and departure dates on the ticket will be about 140 days apart? Should I do anything with the visa before leaving Thailand for Laos and Cambodia?

If you're only going to be in Thailand for one month at a time, you don't need a visa at all. Provided you depart within 30 days, you'll qualify for entry into the country under the terms of the visa exemption agreement Thailand has with the countries in this list

The only exception is if you arrive via a land border in which case you'll only get 15 days.

Thanks. Yes, I know I can get the 30 day entry visa. But, I'll be in Thailand for more than 30 days at one stretch, both at the beginning and end of the trip. That's why I need to find out if the 60-day 2-entry tourist visa will work for me.

Yes the two entry tourist visa is your best choice and there will not be any problem with airlines in that case.

Yes, a double entry tourist visa with a validity of 6 months will work for you. I will be the easiest, if you plan on spending more than one month here on each entry.

There will be no problems with the airlines, as you do have a visa.

You don’t need to do anything when you leave for Laos/Cambodia. Your first entry will have been used up when you leave. On your next arrival your second entry will be activated.

Thanks. This sounds great...