200 psi is badddddd. You could buy a regulator for the portable tank. You could hook the portable tank to a small compressor.
At home I use my small 5 gallon compressor. I made up my own adaptor fitting to connect the compressor to the city water connection. There are two key elements. At the city water connection I first install a ¼ turn hose shutoff valve, I start out by making sure the valve is closed. Then to that I have an adaptor that has an air compressor hose airline quick connect so I can connect my compressor to the adaptor and not have to deal with it. I set my regulator to a low pressure, I like 20-25 psi. To start I open usually the farthest faucet valve (kitchen sink). Once the compressor is charge I open the ¼ turn valve and start pushing the water out. I work my way around to all the faucets and water heater, and so forth. If I feel the compressor is low on air I close the ¼ turn valve and let it charge up again. On additional thing I do is make sure during the blow out process I open all the water heater bypass valves to ensure there is no water trapped on either side of the valve.
You defiantly do not get all the water out using this method, any residual water will work its way down to the lowest points. If the pipe/fittings are not full of water typically when the water expends it has somewhere to go, and not bust your fittings.
You are down south, so blowing out is probably just fine. I like to only blowout between trips if I know it will be below freezing and I will be out again shortly. But at the end of the season, I first blow out the lines then fill them with antifreeze. I to, blow out the antifreeze when all done. It is cold here and I do not like the antifreeze diluted. But as others have said, RV antifreeze is cheep insurance.