I tried slime tubes and found that it was a mess and they were not all that effective. I didn't think it was worth the extra weight or the mess. I also don't like heavy thorn proof tubes. I prefer a fairly light moderately flat resistant tire like the Gatorskin and lightweight tubes. I want a lively ride and not too many flats, but I'll put up with the occasional flat rather that use tubes that can weigh as much as a pound each and will take the nice lively ride feel of a flexible sidewall away.
It is important to use some care in goat head thorn country. Know what the plants look like and any time you pull off the road, check for and remove any thorns. That makes a huge difference. On my first tour out west we had no idea about goat heads and probably had three times as many flats as necessary.
BTW, I used a Bontrager Hardcase for a short while on the TA and it was a big fail. The rubber was soft, sticky, and almost gooey in the 100+F heat. It picked up every sharp stone or piece of glass. I gave up and took it off long before it wore out. It might have just been a bad batch though.
I will say that I have always wondered if tubeless would be a good solution. Going tubeless, I would obviously run some kind of sealant. Never tried it though.