Accumulator tank Size???

[jeffinsalida]

I have a couple of questions for the experienced crowd here. I am going to install a pressure tank and am fortunate enough to have room for up to a 4 gallon tank.
Is there a point of diminishing returns as far as size? ie the small shure flo vs 1-2 gallon or larger? (Does size matter?)
I will install the bypass for winter, will one valve at the tank entrance to close the entry/exit do it?
Should I put a small amt of antifreeze in the tank for winter? I live in the Mountains in Colorado.
If I install the tank horizontally, will the 20 psi of air empty the tank? I am worried about the wieght of a larger tank installed vertically in a 5th wheel trailer breaking connections.
While I am doing this I will install flexible hose and rubber mounts at the pump to help with noise.
Any thing I am missing? Thanks in advance for the help.

[Doug, K4FI]

I've used 2 gallon tanks on all my MH's. Put about 22 lbs of air in tank. It sure cuts down on pump running and gives more steady water flow. I just blow out my lines in winter, but I'm in SC so doesn't get too cold. Here is a link similar to what I use.

Shop Utilitech 2-Gallon Expansion Pressure Tank at Lowes.com