This.
I've recently used both Buyee then FromJapan proxy service, just to compare. Both services offer 300 to 500 yen per each auction bid (that you pay for only if you win). Buyee has optional packing consolidation & extra bubble packing charge. FromJapan has a tool on their website to calculate charges, including for shipping. Here's the damage:
From Buyee, to get 3 dx valks plus several missile packs, tv super pack, and a couple strike super packs (and a couple of super-deformed robots), Total weight 12680 grams, Dimensions 72 × 54 × 46 cm --> EMS Shipping 28200 yen
FromJapan, 2 metal build EVAs, 1 metal build arbalest, 1vf-1j armor. Total weight 4.78kg. EMS Shipping 20160 yen.
What $$ I saved from getting items cheaper via auction, vanishes quickly because of shipping charges.
So don't consolidate shipping for large size items. Combine shipping only for the smallest boxes.