Good math! With you.Well you're way off on the weight and the range. The problem with stacking all the batteries in the trunk is the center of gravity. There's a reason that the battery packs are on the floor in the center of the car. If you want 6 battery packs weighing 40 pounds, that's 240 pounds in the trunk, throws off the driving dynamics although 240 isn't that much, if it was 1200, it'd be a lot. 240 pounds of lithium batteries won't get you very far is the problem. The model 3 battery pack is 1060 pounds and good for 310 miles but EPA claims 272 miles. At 1/4 of that in power, you're now at about 75 miles. So you'd be swapping battery packs every hour or two depending on how fast you're going.
Can you imagine the workout you'd get for swapping out 6 40 pound battery packs? That's not a simple single propane tank exchange. If you want to do the full battery pack on a Tesla, that would be 26.5 40 pound packs or more. Not too many people out there would want to move 40 pound packs a few feet 26.5 times. People on average are way too out of shape for that. Also keep in mind that Blue Rhino puts in 15 pounds on a propane tank so a full propane from them is about 32 pounds instead of 37 with a real full 20 pound tank.