I made the move to Portugal a little over 9 years ago.
I had a long wheelbase Transit and a big box trailer and i was moving myself. To make sure everything would fit.Here's what i did.
I owned a Franchise with the UK's largest off license chain so i had access to boxes plenty of boxes. Moving about 40 pallets of wines, spirits and beers i knew all about packing.
I found that the best boxes where for a Chinese beer and a Mexican beer the boxes where the same shape and size.I filled everything that would go into a box went in a box. You could use any odd size boxes you can get but will it all fit. I ended with over Fourty boxes but no wasted space.
So if you plan to move and do it yourself make the best use of the space you have.
I sold the trailer to a local builder and drove the van back to the UK to sell and collect my car.
Good luck with your plans.