Go to the nearest Surplus store and buy some body bags. I have a couple that I put deer in when i have to use my wifes Explorer. I also have the cargo tray as previous mentioned. The bags are just extra insurance. My wife could pick out a spot of blood from a mile away.
I bought a large rack for the back of my SUV. It is 24"X60" and has 4" high sides. Fits into the 2" receiver under the rear bumper. I put an 8'x10' cheap PVC tarp on the rack, pile on the deer, then wrap it over him and tuck the excess tarp underneath. A few bungie cords to keep the tarp down when hitting highway speeds and your done.
No dirt or road grime gets on the deer and non-hunters are not offended even if they can guess what inside of the tarp.
Another thought. I have previously purchased through a mail order house(can't remember where) very large and strong game bags. They were made of heavy plastic and could hold an entire deer and still be closed tight with a wire wrap.
If you must put a bloody, bug ridden deer in your wife's truck, I'm sure that she would appreciate you bagging it completely. Maybe someone on this board knows where you can get a few of these bags.