as long as you are stationary, your legal for the higher output power. It isn't home or not, it stationary or moving. That's why the weboost high power RV system uses a external temporary mount antenna. Let's them meet the requirement it won't be used when moving.
Now, in any case you do need to have adequate separation between internal and external antenna to avoid feedback and oscillations.
Now, also make sure you have the correct impedance antenna. most mobile car systems use a 50 ohm antenna. While many home and RV systems use 75 ohm antenna. The 75 ohm advantage is much lower loss in the cable for reasonablyt priced and flexible cable.