There is a public slip at port glasgow (Newark Castle) which will be fine for an ordinary car with a SR4. It can get very slippy with weed/slime. It is usable about 3/4 of the tide - but becuase of the slime I suggest you use a rope unless its close to high tide. If you intend to tie up to the pier then be aware the ladders are only long enough to use at about 1/2 the tide and they are covered in razor sharp barnacles which will do bad things to tubes.
Possibly not the best place when you are having engine probs though - as rarely anyone else around to tow you back if necessary.