FWIW
I would not use a trash can.
I boondock exclusively. I have a gravity fill freshwater tank. To date, I've toted 4 x 7 gallon reliance jugs full of potable water, and I made an adapter for one of the caps using a 1/2" npt to barb adapter, some clear 1/2" plastic line, and a hose clamp. I dump from the jug into the fresh tank.
But, at 60 pounds each, carrying, lifting and holding the jug as it empties is getting to be a challenge at my age.
So my plan...which is in line with your concept...is:
I can fill this anywhere...home or at an NFS spigot/hydrant and so on. I will use 120 volts for the pump, because I have a generator, so may as well. But similar 12 volt pumps are available.
Why spend for the tank? It's certified for potable water. It's sturdy (whereas a 30 gallon rubbermaid can is not). It's sealed so it stays clean. Moving about with a full load of water, the water won't spill and the can won't tip over and dump. The tank won't split or rupture from the weight of the water as the trash can might. The pump makes the transfer easy and clean. The whole system can be sanitized as one would sanitize the fresh tank and RV plumbing. Last but not least, the entire system, tank-pump-plywood, will weigh in at about 40 pounds or so dry. One can simply toss the system into the bed of the truck and fill, then remove it easily when it's not needed.
You can get a 25 or 30 gallon version of this kind of tank. Bear in mind that water weighs 8.3 pounds per gallon. 50 gallons weigh 415 pounds. 30 gallons weigh 249 pounds. What you can haul depends on your TV's capacity. I routinely always haul the 28 gallons in my 4 jugs so I can drink water from home rather than take pot luck at some NFS hydrant. My truck handles the nearly 250 pounds of water with ease.
The links are illustrations, not recommendations. Potable water tanks and pumps are available from many sources.