I have read that in order to successfully enchant constant effect items one needs to have Intelligence and Enchant up near 900 pts. Suggestions I've seen include making custom spells which have:

Fortify XXX (where XXX is the skill or attribute)
Self, 100 prts, 3 secs

repeated 8 times

When I try this with the Enchant skill, the chance of success for the spell shows as negative (-4) after adding it only 5 times to a custom spell. I assume my chances of casting the spell are thus nil. Is there some requirement for doing this successfully? I have over 100 Intelligence right now, and my Enchant skill is 50.

The amount of Enchanting skill or Intelligence needed to successfully enchant constant effect items is based on how much enchantment points your enchant requires.

The known formula for the chance in percent is:

Enchant + .25*Intelligence + .125*Luck - 5*[enchantment points]

So, saying you're fine with 900 Intelligence is wrong. It's all about how expensive your enchant will be. Given the formula, you'll be able to find out how much Intelligence or Enchant skill would be needed. As you can see, Enchant is worth 4 times an Intelligence point. Find out, what values suit for you based on what you already have.

Thank you! That helps a lot! And I figured out how to make & use the necessary spells.

The formula is different for Constant Effect verus other effects. The penalty for Constant Effect is twice the formula penalty other effects.

The formula listed is for Constant Effects, but other effects use a 2.5 multiplier in the formula.

The formulas are very useful. Thank you!

havent plaed in a while,so I take it from memory.
Fortify spells is based on restoration,so I have one safe fortify restoration spell to buff it up some,at buff-level I maybe have it at 80%-90% spell-chanse a second fortify restoration spell,after that you should be able to go wild with other resoration based spells,or do a thirdh buff
Works also with enchanted items (belts,rings,amulets,paper). A little fun cheat is to give paper improved enchaning point,makes it more useful,still cast once though.
Naturally they get enchanted with fortyfies.Are also some items that can help out spells and enchanting,imperial cult hands out some,and then there is the sanguine items.

Yes, as you suggested, I had to use 2 restoration spells to get to where I needed to be effective at enchanting anything for restoration. And I haven't found anything on the Sanguine items yet ... I guess I'll also need to join the Imperial cult to see what those items are. Thank you!

The sanguine items is in a quest in morag tong,where you supposedly should give them back,can help advances if you do,can help you if you don′t
nothing terrible helpful,mostly 5 pts CE.
http://www.uesp.net/wiki/Morrowind:Sanguine_Items

Imperial cults ones is actually quite nice,you need to advance a fair bit though to get them all.
http://www.uesp.net/wiki/Morrowind:Unique_Clothing
You are after akatosh ring,maran amulet,stendarrans belt, which is best suited for the topic at hand,they have a lot more usefull stuff of course,septim ring helps speechcraft to mention one.
While we are at this,a fortify luck spell/potion doesn′t hurt either,even if enchant and intelligence is more important