I have now start to Building a frame,I will use 10MM PE 1000 GREEN (UHMW-PE) (will float in water)
To weekend,I will mill out and assemble frame.
On the cast tube,i will use POM-C (acetal) to make Caps. cast tube have a wall thickness of 6.25mm,so i dont need to be worry about any leakage,I will use my lathe,to make a track on both side,and use o-ring.(not inside) (I most have a rod (bolt),but you will get the tube 100% watertight.
Frame size will be: L 450mm X B 290MM X H 250MM
Here is some new picture of the finished tube, i have only test this,in a water tank, no leakage.(maybe,i most have o-ring inside to,you can see on the picture,these o-ring is push together to the tube,i think it will stand a high pressure)
![Image](http://imageshack.us/a/img692/1074/92100695.jpg)
![Image](http://imageshack.us/a/img692/1513/13568168.jpg)
![Image](http://imageshack.us/a/img600/3108/imgp1087p.jpg)