I've motored across the Channel a few times in a 22' boat, though a bit to the West of Dover ( a longer trip though ).

I'm, sure you know the old method of taking a hand bearing on an approaching ship; if the bearing stays the same, you're on a collision course - so make it plain you are altering course to go behind.

Binoculars with an integrated compass are very handy.

Once when unforecast fog descended mid Channel, I had to tack to & fro all night in the separation zone, very tiring but infinitely preferable to bimbling across a shipping lane blind !

Do have plenty of fuel - to motor the whole way if necessary; my 5hp 2 stroke gives 2.5 hours per gallon at 5 knots.

Setting off in the dark is preferable to arriving at night; people say 'it's much more obvious at night' but that's assuming the lights are all working !