The styrofoam chalets were very effective in my small test last year. Specifically, 7 of 8 were chosen by martins and fledged young. Two chalets were in Alberta, two in Texas, two in Oklahoma, and two in Tennessee. So they were equally effective with one inch styrofoam in the heat of the south as well as the cold of the north country. The problem with them is that they were just "too lightweight". As they were under one pound each, and had a lot of wind resistance, they blew around too much in a strong wind. The way around this is to mount them solidly, or to use a wooden floor to add weight. They are also more difficult to hang, being a rectangle. But the martins seemed to like the inside dimensions of 7" x13", and the one inch foam. In this photo the covering was not epoxy/cloth but rather the plastic "signboard" used for outdoor signs that looks like a sort of "plastic cardboard". The entire back comes off for nest checks, and is held on with two butterfly toggles.
Another chalet that worked very well was made of either 6" metal stovepipe or 5" stovepipe, arched over a 7" wide board, and insulated with either Great Stuff insulation, brown outdoor carpet (only on the inside arch), or a couple of rolls of cork. The advantage of the metal stovepipe is that it would be virtually hail proof, but so would styrofoam with cloth/epoxy. There is an S&K access port on the back of each for nest checks. The inside dimensions are 7" x13", and with the 1/2" wood floor, you can extend it as in one of the chalets, and it doubles as a porch. With the wood floor, these chalets are heavy enough to not be bothered too much in the wind, similar to a plastic gourd. Sorry for the rough front to the stovepipe chalets. I was experimenting with additives to epoxy, and the lumps were just too hard too sand off, so I just painted over them. The martins won't mind
And I can't find my photo of the "pretty ones" right now, but you will get the idea from this photo. Both ends are 1" styrofoam. Last year chalets very similar to this were VERY successful in attracting and fledging martins.
The stove pipe idea is great. I have been thinking of other alternative forms of housing for the Martins and Bluebirds. Do you think using PVC pipe cut in half lengthwise would work? It would be heavier to be sturdier in winds.Or how about the cardboard forms used to make cement posts or columns?? I'll check out the hardware store and let you all know what I come up with. Keep using those brain cells before they are lost. 