Similar situation here in WA state. I knew I would have to register my DIY
boat before I could document it and the Dept of Licensing had given me a
flyer several years earlier. It stated that I would need to provide the
reciepts for material and equipment at the time of registration so they
could establish the value and assess the tax on any portion of the value
that hadn't already been taxed.

I had a filing cabinet full of reciepts, both from WA and out of state
purchases, some taxed some not taxed. Prior to submitting these, I inquired
about how they wanted me to present these reciepts and was then told to just
bring in copies of the reciepts for the major equipment (engine,etc).

However, for some reason, I made copies of all my reciepts. I went to the
DOL office with all of these. They were a bit surprised but excepted them. I
had even done adding machine tapes with the material totals and sales tax
totals. Then, since the boat wasn't finished or fully outfitted, we agreed
on a modest value declaration. (I argued that the sales tax would be paid on
any subsequent material/equipment.) From this declared value they subtacted
the total of all the reciepts and I paid the tax on the difference.

What makes this strange is that I paid tax on my labor and I paid tax at a
rate of 9.5% (the current rate) rather than 8.5% that was in effect the
previous years. (Even though I had paid sales tax on the material, they
charge me 9.5% on the overall declared value of the boat and subtacted the
total sales tax paid previously at 8.5%.)

Had I not provided all of those reciepts, I would have paid a much more
using their methods (major equip, etc.).

I could have registered the boat in early stage of building, when I
purchased the bare fiberglass hull. But then the boat would have been
registered as built in 1995 rather than 2002. (as if model year has much to
do with a DIY boat)

I won't say what I paid in sales tax, but it would have paid for a new main.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions