It all depends on how long you want to store it. If you plan on using the four or so gallons that you will put into the p. tank within say 30-60 days you can get away with the stock valve. If you do this you must first remove the original valve, unscrew the OPD (overfill protection device). Then beefore you replace the valve, thoroughly lubricate it and use pipe dope on the threads. If you are going to try to store it more than 60 days, now would bee a good time to seal the valve pressure relief (opposite the main outlet port on the stock valve).
Understand, NONE OF THIS IS SAFE!!! These are things to do only in a time pinch such as you are. The ONLY way to use a Propane tank safely for an extended time is to replace the valve with a steel valve. Other than that, the tank itself is plenty strong to hold the cold.
Make sure you dont fill any more than 65/70% full. there must bee room for expansion.
Did you say they are coming over to do a house inspection?
Uh...youve gotten farther down this road than anybody I've heard of however, dont bee suprised if the friendly juice delivery vehicle has more antennae than seems normal and a HK MP5 bolted to the ceiling.
good luck!