I'd recommend consulting with your local VAR or Ruckus SE, who can best understand your environment.
There could be an impact from making changes on the AP side. To "help" clients make their roaming decisions
sooner, the 'bss-minrate' on the WLAN used can be increased from 2mb to 5.5mb or 11mb, which reduces the area
around the AP for clients to receive probe/join responses, and should encourage them to look for another AP sooner.
Does it help if you roll down the vehicle windows? Or use your laptops on the Dash, instead of from the seat or your lap?