Your strategy might work, poorly, if you leave your vehicle outside of whatever clear_area radius is specified by the mission to make sure there is nothing in the way when it starts creating objects, vehicles, and actors. If CJ's current or previous vehicle is caught within the clear area radius it'll get sent to the nearest impound garage, other vehicles are simply discarded.
Other issues involve required mission vehicle bumping CJ's previous vehicle off the memory list. And San Andreas isn't all that reliable about keeping discarded vehicles in memory anyway, even the most recent. I expect this to be a frustrating process but you may as well give it a shot. Trying unusual strategies just to see what happens is how we keep learning new things about this game. Maybe you'll learn something cool.
Hey Orion its Jack here. I remember a long time ago asking about Berkeley RC van for a starter save file. Im screwing around on a file before the first mission again and reading this topic got me the idea to use Big Smoke to store/impound aircraft nicely. For instance after collecting police bribes you can start Big Smoke in a Police Maverik, Cropduster, or any other aircraft that will fit in the impound to store it.
Here is what is useful about the mission though, if you want to retrieve those vehicles you can go into the impound during the mission and set off the alarm, but you will not receive 3 stars! So thats sorta useful for players who don't mind setting off the whole beginning audio thing. Also I went hunting for a tow truck down near the docks,and I found Berkeley's RC van driving there. Had no idea it would spawn that easy, could being on a mission change the odds of what spawns?
Anyway as for the topic, someone mentioned different vehicles have a better chance of sticking around. You guys think aircraft should have a higher chance, since they appear reliably in the impounds over cars and bikes? Im also experimenting with using different vehicles during the cutscene in montgomery, where Ryder and Big Smoke meet up and Sweet gets chased off. Its pretty funny having Ryder telling CJ to keep up while he is sitting in a Seasparrow.