It's a shame you live at at the opposite end of the country, because I'm one of those "few and far between" individuals who make a living with traps and snares, and always ready to help anybody who is serious about learning the skills of trapping. Just be careful not to fall foul of the law.
The only traps that can be used legally (other than mouse/rat traps) are listed in The Spring Traps Approval (England) Order 2012, and similar regulations for Scotland and Wales. Improvised traps of the type found in survival books are illegal, and could land you in court with the possibility of a massive fine or jail time if convicted.
The most important knowledge needed for successful trapping is not knowing about a wide range of traps, but about the biology and behaviour of the target species. You also need to know what other wildlife is in the area, because if you catch an Otter in a lethal trap set for Mink, you are in BIG trouble.
If you do come across a problem you can't find an answer to, PM me and I'll try to help.
Alan