My husband had a multiple entry visa and it was expired 3 months ago, and when we tried to extend it he only got 30 days visa. Now he has to extend it again, what paper will he need to get his visa extension?

Tell us a bit more. Are you Thai? If you are Thai do you have a registered marriage? Are you working here? What kind of visa did he have (it seems to have been a tourist visa and a normal 30 day extension)? If you are Thai can you prove a 40,000 baht per month family income?

Have found you are Thai and you and husband are running a business and have not been able to extend in attempts last year. What is his current status? Is he really on an extension of stay and has work permit? (you say 30 day visa which would not allow a work permit). If he and you can prove the 40k monthly income he should be able to extend with TM.7, 4x6 current photos, bank passbook/bank letter (matching balance), passport/arrival card, your ID card, your home register, photos together at home and some outside home showing number and copies of everything. He would apply for a family extension of stay.

Yes Lopburi but the extension of stay would not be granted now (I understand) as there is (apparently) no history of tax payments made on 12*40,000 in the preceeding 12 months.

Seeing as he was given a 30 day extension, one must assume, as you say, that he was on a multiple entry tourist visa. It has been a long long time since anyone got a 30 day extension on a non immigrant visa. 7 days there would be the normal maximum.

So I thikn he is stuffed for the marriage extension unless they are paying tax on 40k or can go to a friendly amphur and pay "back taxes" to get the tax forms which immigration will want to grant such an extension.

One point I am not clear on is whether he can go from a 30 day extension to a tourist visa or from a 30 day entry stamp (if he does a border run) to an extension of stay based upon marriage and tax paid on 40k. I suspect you can but I am not 100% sure that you don't first need a non immigrant visa.

In previous post it was said he had a multi entry non immigrant B visa and they had paid tax last year but it is hard to keep track and have no idea if the 30 days may have been the normal extension of stay under review period or something else.

You always need a non immigrant visa to begin one year extensions of stay - but they can be issued by Immigration for 2,000 baht if you meet conditions.