Hi Chris
I have been moored in Sunderland for coming up 5 years, It's not the cheapest mooring in the area but access at all states of tides with no locks or barrier gates to worry about and easy access to some great marks without a long steam to get to open water.
It is quite tight in places and like yourself my previous boat ownership was trailer launching, although much more expensive I would not go back unless I had to.
Some boats do suffer with water build up after very heavy rain, I have a self draining deck so not an issue for me, the marina is manned 24hrs and the lads regularly check the boats for problems and are pretty good at letting you know if they think you have an issue. If you have a decent cover and are prepared to check your boat regularly you shouldn't have any major issues.
Good luck in whatever you decide!
Cheers Dave