You may want to look into a pop out monitor that fits into a 1din opening. You can hide one of these in various places depending on the type of truck you have. You could even take the cover that folds down and glue something to it so when the monitor is folded in it is hard to tell it isn't a normal part of the truck. Otherwise your best bet is to hid it behind a panel that is removable. A removable panel could be done reasonably easily too. Just get an HDMI monitor and mount the bracket in your truck in a manner the screen is removable. Then you just hide the cables somewhere in the dash when not using it. Most monitors you can mount in your vehicle will have 12 volt plugs on them. Anything else won't be as easy to remove. Be aware that you may wear out the socket if you unplug and plug the plugs all the time. You may want to get extension cables for each that you leave plugged into your monitor so the cables can wear out where they connect together which is easy to replace. A worn out socket means you try replacing the socket or the monitor.