I've only had my first drone, a P3S, since April, so take this with the proverbial 'grain of salt' lol...
I wanted to do the same as you, and the only way I've found so far is with an Nvidia Shield K1 tablet, which has a mini-HDMI port. I now have a K1, and a 10' cable with mini-HDMI plug on one end and 'full-size' HDMI on the other. So I run a 20" flatscreen TV in my work van off a 300w inverter. Works great and people are amazed that they can stand next to the van with the side door open, have a real-time FPV birdseye view, and can watch the bird at the same time!
edited: As a bonus, the K1 will also 'Cast' wirelessly to my 48" living room TV. So I can stand on my deck, fly my new P3 Pro, and it displays inside on the LR TV... cool! That only works with the P3P tho, since the Tab and TV both have to be connected to home wifi.