For days out I just use a basic cheap rear door/boot mounted rack. Instead of the supplied soft foam, fit foam pipe insulation (from B & Q etc - the thicker the better) on rack tubing where it contacts, or might contact, car body and cycle.
There should be no problems with obscured lights and number plates on most saloons and hatches.
Just make sure the lashings are tight (at start, at petrol stop - and every other stop).
Use a few bungees - to prevent front wheel and pedals damaging paintwork.
All this for a fraction of the cost of fitting a towbar/roof rack and expensive carrier.
- No space problems for up to 3 cyclists/bikes I find.