I suspect the pipe in the plans is not the 2" water pipe I visualized.
the first landyacht in the plans used a special high quality type of 2" tube used in the mineral exploration industry, it is a hollow drill rod used in "diamond drilling" this is the method of drilling used for obtaining core samples.
The pipe has a hollow, diamond dust coated drill bit screwed onto one end, and while spinning at high rotation with water being pumped through it is forced into the ground.
If there is any mining exploration in your area you might be able to trade a carton of beer for a couple of 3m lengths.
the second landyacht used standard steel tube- as used here for road signs, fencing and general engineering works.
A similar type should be available worldwide.
Its a bit bigger in diameter, a bit thinner in the wall, but easy to work with, and most importantly- easy to find.