I try and avoid extended payment structures any more if i can help it ( invoice then 30 days from end of month)
its just not wort the risk , Did a large extension with swimming pool and snooker room for a local builder at the beginning of last credit crunch, 5 weeks before xmas and things were very tight but we started the job under usual terms, then got wind the builder was going under, so pulled all the lads off site, builder turned up promised me no problems at all and gave me a chq for a couple grand, and after loads back slappin on his behalf we carried on , two days before completion he whent bust , this was the week before xmas and all the lads were expecting to get payed, stopped work again, and then the house owner offerd to pay if we completed, so we completed ,invoiced house owner for the £17.000 and he refused to pay saying he could not because my contract was with the builder, so had to pay all the lad,s the materials on accounts and it left me with a very merry xmas, and this was for a builder who we had a great rappore with, there are a few contractors who i have 30 day aggreemants with at present, but its rarely above a couple of grand and if it does they Jobs are split into stages and invoiced per completed stage.
My point is it is inevitable you will get stung one more than one occassion, but try to limit any damage by agreeing weekly payment or staged payments, it does not matter how well you know them or how good a reputation they have they still could be strugglin to pay and this can put in serious jeopordy, so don't be afraid to ask for payments upfront or at stages wherever possible, if they have nothing to hide or worry about then they will agree your terms and not theirs.
Suppose we could all go on writing for pages about the pro's and con's but i am sure you will be able to extract the advice that you kneed from this and previous postings.
Regards Paul
P.S if not then get a job in the civil service , much safer