Custom Built MH & basements

[Tina]

I have been searching MH builders on the net and have been looking at the structural integrity of the homes. Many (almost all of them) of the builders do not show the actual building specs on their website. When I do find a builder that has what I am looking for, the home is not available in the geographical area I am interested in (Longview, Texas).
My first question is: Can you have any MH builder custom build a home for you with the structural integrity you want? i.e., 2x6 or 2x8 exterior walls, double or triple header above exterior doors and windows, and R21 insulation in walls, R21 or R33 in floor, and R38 or R40 in ceiling. I have seen several floor plans I like in the Patriot Homes and Clayton Homes. Do you know if these builders will custom build a home to the specs I want? Or do you recommend a builder who would?
My second is: I currently live in the midwest (Illinois). Basements are very common here. However, I have been told that basements are not that common in Texas. Can anyone tell me why?
Thank you.

[Danny]

Tina , there are none that I'm aware of manufactures build "their" standard home and then have "their" upgrades and options

[Lee]

Texas and southern homes do not need a basement to have a foundation below the frostline, so virtually all stick-built homes are slab-on-grade. Coastal area have too high of a water table to put a basement. Therefore, hardly anyone is in the business of building basements