Enchanting - please help Options

[Magefire]

I've started playing Morrowind again, and I need a longsword with soultrap. I can't find any advice online which answers my difficulty.

I have a grand soul gem with a Clannfear - I know, it's not very good - and a silver longsword. I took myself off to Galbedir and asked her to enchant the sword for me. Despite her efforts and my cash, it didn't work. Luckily I had presaved.

I chose 'cast when strikes' and set the duration to one second on touch. As to 'area' I wasn't sure if this is needed since the spell is 'on touch' - I set it to zero. Was this a mistake?

Also, if I get a stronghold I'll be awarded an ebony longsword - if I enchant it with, say, fire damage, Cast when Strikes, what 'area' do I select?