A large lizard in a sealed tub has two opposite ways to be harmed: too little air exchange, or fresh air arriving as a cold stream across its body. The fix is about placement, not quantity — ventilate from above the animal, so air turns over gently in the top of the tub while the layer of air the lizard actually lies in stays still and warm.
Where the Holes Go, and How Big
Drill or melt a band of holes around the upper walls of the tub, above the height of the lizard lying flat, and add ventilation in the lid itself — a mesh panel or a cluster of holes works well. Warm, stale air rises and leaves through the top while cooler fresh air enters high and mixes before it ever reaches the animal, which is exactly the slow, indirect exchange you want. Avoid the instinctive pattern of low holes on one side and high holes on the other: that cross-flow ventilates efficiently but runs a continuous draught along the floor of the tub, straight over a lizard who cannot move out of it.
Size matters for safety as much as airflow. Holes should be small and smooth-edged — large enough for air, far too small for the lizard's head — and check every edge with a fingertip, because a big, strong lizard will push claws and snout into any opening while travelling, and a claw caught in a rough hole can tear. Mesh must be secured so a determined animal cannot peel it back, and any tape belongs on the outside of the tub, never where skin or claws can reach the sticky side.
In the Vehicle: Airflow Without the Blast
Position the tub away from dashboard vents, open windows, and door seals — the places car air moves fastest and coldest — and settle it level so the lizard is not braced against a slope for the whole journey. A digital thermometer with its probe inside the tub takes the guesswork out: glance at it at stops rather than opening the lid at every pause and dumping the warm air you have worked to keep. Shade the tub from sun through glass, which can overheat a ventilated tub as surely as a sealed one.
In cold weather, slow the exchange rather than closing it: drape a blanket or towel over part of the lid, or set the tub inside a larger insulated box, leaving some ventilation uncovered, and check the thermometer more often. Never tape over every hole, never use a fully sealed container "just for a short trip," and never leave the lizard in a parked car whose heating has stopped — the tub's stable temperature lasts only as long as the car's does. If the lizard is restless, scratching at one spot, or gaping, stop somewhere safe and check temperature and ventilation before assuming it is simply travel nerves.
Sharing the hole placement, the in-car position, and the temperature range in KinsLe's Care Pass means a sitter, friend, or family member moving your lizard sets the tub up draught-free the first time, without learning it by trial and error.