My son has used an NG tube since May 2011! So lots of experience with it... But before you get scared at the length of time , let me explain...
He was 16 when he started, did six weeks of the formula only through the tube and, since then, has continued with the formula on a supplemental dose as maintenance (until very recently).
He was taught to insert and remove the tube himself, so would insert it nightly and remove it in the morning. It truly wasn't very hard for him to learn and, within a week, was taking him just seconds to do in the evening (removing it is very easy... it just slides out). (But, keep in mind, everyone's different, some people do have a harder time with the insertion and choose to keep the tube in.) I agree that the size of the tube is important... Stephen's tube is 6FR - this is apparently infant/child size BUT, Stephen's 5'11", 170 lbs and it works fine for him! It's about the size of a piece of spaghetti. It's also very flexible.
The toughest part is getting it past your gag reflex... while they/you are inserting the tube, drink some water (through a straw), as you swallow the water, you sort of swallow the tube at the same time. Once past that point, it's then much easier to continue inserting. Sometimes it is also easier to use one nostril compared to the other. My son ALWAYS uses the left side.
Now, why my son is STILL doing it... The exclusive period (six weeks of no food) helped him tons!! It took away his symptoms, he felt great, got lots of energy back, etc. His doctor tried to use EN as a maintenance treatment - so, after the six weeks, he added back a regular diet but continued with the EN 5 nights a week, at half the dose. He has done this since. He hasn't had a flare since diagnosis, however, MREs show that there is continued inflammation in his small intestine. To treat the inflammation, he recently started remicade. For now, he is still doing the supplemental EN with the remicade but we are beginning to reduce it so that he's done with it within the next few weeks (before he leaves for university).
If you absolutely cannot tolerate the NG tube, there are also drinkable versions of the formula... Peptamin, Elemental, Modulen. From what I have read, they are tolerable but, perhaps, not great tasting. (IF you can learn to insert the tube yourself, that could end up being easiest... given the choice, my son finds the tube easier than drinking a bunch of shakes.) One downside to doing the overnight tube is that you will have more hunger during the day (as you get all your 'food' overnight); the shakes give you the flexibility to drink one whenever you're hungry. To alleviate some of my son's hunger, he was allowed clear fluids (gatorade, ginger ale, jello, freezies, broth, etc.) - this really helped.
Here is a link to another thread, Kids on EN, in this thread, I included a link to a youtube clip showing a girl using an NG tube. She is very precise and shows you EXACTLY how its done (one comment, she is SO precise, it seems to be a long process - truly, it takes my son 10 seconds to insert the tube and a few more seconds to tape, etc.)
http://www.crohnsforum.com/showthread.php?t=36345