How are people doing campers with Tacomas and not blowing their GVWR?

It's because at the weight and size of a small truck a good chunk of fuel economy comes down to weight and aerodynamics not the engine size - to a point (really small and light vehicles larger engine size is really detrimental to fuel economy). It kinda makes some sense if you think about it - a really small engine would have to work quite a bit harder to move the same truck as a large one and would very likely get worse economy. For a smaller car a really large engine is essentially wasted energy etc. I'm sure there's some calculus formula out there that can figure all this out for an automotive engineer (weight, drag coefficient etc). I saw a video recently that shows that fuel saving devices don't really do much but the way you drive actually does (in other words are you the kinda person who is a lead foot or do you feather the throttle after coming from a stop). Contact surface makes a big difference as well - freight trains get over 500 miles per gallon per ton: https://www.csx.com/index.cfm/about-us/the-csx-advantage/fuel-efficiency/ (it's kinda of a weird number for sure but freight train will get about 1-2 miles per gallon but actual economy at 10,000-20,000+ tons gets pretty hard to measure using conventional methods). The reason is the contact surface for traveling is about the size of a quarter per wheel - but that has some downsides in that trains typically can't handle to much of a steep grade. This is why making sure your tires are inflated properly does help with fuel economy - or why on your bicycle the higher pressure the tires the faster you can go.