hey gnome, that is nice!
advantage being that bike was intended to be ridden over long(ish) distances, hence the adequate seatpost, unlike a BMX...
I still think using BMX frames is fine, and am decided to try it. I am thinking about seatpost isssues mainly such as:
-is there generally a size (diameter) BMX seat tube, or do they come in a wide variety as most bikes do?
-what materials and gauge of tube would best ensure safety with an extra long seat post?
where can I source said seatpost/tubing?

other concerns also come to mind such as:
-will most BMX frames accommodate a standard cartridge bearind square tapered bottom bracket?
-will I be able to fit the right stem to a standard BMX fork, or will I be better off fitting a road-type 20" fork from another source?

all these questions will be answered by doing, but if anybody can share some of their experience it would sure save me some time and effort!

thanks!