That is a good tutorial...I saw it awhile back.
I had over 80 inline splices to do this year to get the spacing right on some cheap lights I bought. I found the heat shrink tube at Harbor Freight to work great and they have lots of sizes, dirt cheap. I used a heat gun on low setting and got a good seal every time. With SPT1, you can use a piece of 1/8" tube for each wire and leave them separated it like that, or use a piece of 1/8" on one wire, then slide a piece of 1/4 over both to make a clean looking splice.
If you are splicing wires that also have a thick weatherproof jacket (like I had to), you have to get a good seal on the jacket, while making sure that the soldered splices inside the heat shrink don't touch each other. Building them up with electrical tape is OK if you have just a few, but I tried something new and it worked great. Little pieces of Tyvek, the white house wrap stuff.. I keeps scraps of it around that I've found a t jobsites. I just put a little strip between the bare wires, fold it over, slide the shrink wrap over the whole thing and seal it all up. The Tyvek is like tough plastic that won't let the rough solder splices rub through and short out like they can with tape sometimes.
Good Luck,
Mike E.