"Off the top of my head"...
Make sure local codes will allow you to do this.
Assume this will not have
plumbing? I.e no running
water and maybe a composting
head?
Assuming you will partially bury the
hull for easy accessibility, how high is your
water table and what are your soil conditions? If you bury it, and the water collects around it, it's going to want to float. Frost may also be an issue, and can also force the
boat back out of the ground. You will also have to consider drainage and
plug all the thruhulls, or water may leach back into the
boat.