Floyd Mayweather dropped $300,000 on an insanely luxurious customized Mercedes party bus … with a HUGE TV and BAR … and had it shipped across the desert last night … TMZ Sports has learned.

The whip … a souped up Mercedes-Benz Sprinter a.k.a. “Land Yacht” … was designed specifically for Floyd … and it’s AMAZING … even for a guy with an RIDICULOUS car collection worth over $7 mil!

The specs … 55 in. TV with Apple and Direct TV, Surround Sound stereo system, Maybach heated massage chairs, Champagne bar, and cabin lighting system … to name a few.

Our sources tell us Floyd wanted the party bus last night … so Fusion Luxury Motors in L.A. … who acquired the Land Yacht for the champ … delivered it from Cali to the boxers Vegas mansion.

Check out the pics … there’s a reason they call it a Land Yacht.