Water tank for 1963 Greythorne

[Greythorne Special 14]

Hi all - seeking information about the installation of a new water tank on a Greythorne we are rennovating/rebuilding. Existing tank is metal and lined with rust so needs replacing. Its currently in the the main seat - so takes up valuable storage space. So, looking at an under-van water tank, probably 60L. The ones i've seen are around 18cm in depth. The clearance near the axel is 38cm.

So my questions are:
has anyone fitted an under-van tank?
If so, are you happy with it?
Is the clearance enough to fit one?

Thanks in advance!

Nick & Tracy

pics here:
s1336.photobucket.com/user/trayhead45/library/Caravan%20Restoration%202014?sort=3&page=2

[Franklin1]

Well, I don't wanna dob anybody in but you could probably have a read of this post.