If anyone is wondering, yes you can fit a 70" boxed TV in a Prius.

I was able to fit perfectly a 70" TV in its original box, tilted while entering the car and then laying it flat (apparently not recommended but I had no issues), so I was able to close the hatch! (Prius 2015). Very roomy car, I have carried mattresses, couches, even live trees! I don't think a 75+" TV will fit, probably the 70" is the limit.

 

Try a 40 gallon boxed water heater...I did and I closed the hatch to boot. If you’re British either way will work.

 

Most would probably think that you would maximize the space by putting the front seats forward.

I actually found that you get the most space by putting the backrest of the front seats all the way down. It would be difficult to drive and would be a bit dangerous. In the case of the TV, I would lean against the box instead of the seat backrest for the short trip home.