I would just line them up manually and then maybe put a plain box around them on the outside. You could even kindof "merge" a box with each terrain at the very lowest point of each, so that when you put it in place, the seams are perfect....

 My Rendo-Space 
Do you know where your towel is?! I love Vogon Poetry. :P
DON'T PANIC!

Portland Pirate Festival Arrrr!